On first sight it seems that there is little to discuss here. Showing favouritism seems opposed to treating people fairly and equally, as the Christian principle of the Sanctity of Human Life seems to demand. Famously, Jesus taught “Love your neighbour as yourself” (Mark 12:32), suggesting that Christians should love all people equally and not prioritize one group over another, and his brother James clearly wrote “…believers in our glorious Lord Jesus Christ must not show favouritism…” (James 2:1). Nevertheless, when in 1968 CELAM’s Medellin conference called for what in the same year Fr Pedro Arrupe had called a “preferential option for the poor,” many Christians responded, agreeing that Christian teaching on social justice demands that the Church should prioritize the poor. Further, in recent months many Christians have supported the “Black Lives Matter” movement, which seeks to prioritize black lives now to address the fact that these lives have long been ignored. On closer examination it seems that there is a lot to discuss here, not least because the ideas of favouritism and prioritizing one group over another have been conflated in the question, when in fact – as Stephen J Pope argued in 1993 – they are distinct. In reality, it is true that Christians should not show favouritism, but that does not mean that they should not prioritize one group over another.
In his article “Proper and Improper Partiality and the Preferential Option for the Poor” Stephen J Pope opened by acknowledging that “the preferential option for the poor has become a major theme in contemporary Catholic Ethics.” The theme is often attributed to the influence of South American Liberation Theology from the late 1970s, but as Todd Walatka argued persuasively in 2015, the origins of the preferential option for the poor are really in Vatican II documents “Gaudiem et Spes” and “Lumen Gentium” (1965) and Pope Paul VI’s “Populorum Progressio” (1967), which predate CELAM’s Medillin conference in 1968 and Gustavo Gutierrez’ “Towards a Theology of Liberation” (1971) and far predate the famous articulation of the concept in CELAM’s Puebla conference in 1979. In this way, Christians have long argued for the poor to be prioritized as a group. Indeed, there is good Biblical justification for prioritizing the poor. Arguably, Jesus himself gave a preferential option to the poor and to sinners; he chose to become incarnate of an unmarried mother and to live as and with the poor. In a society that saw wealth as a reward from God and misfortune, including poverty, as a sign of sin and God’s displeasure, he rebuked those who questioned his spending time with sinners, saying “It is not the healthy who need a doctor, but the sick. I have not come to call the righteous, but sinners…” Mark 2:17. Of course, he might have meant that the righteous and, by implication in that society, the wealthy were in no need of his help as they would achieve salvation anyway, but in Mark 10: 23, 25 Jesus remarked “How hard it is for the rich to enter the kingdom of God!”… 25 It is easier for a camel to go through the eye of a needle than for someone who is rich to enter the kingdom of God…” as if wealth is a barrier to salvation. This suggests that God gives a “preferential option” to the poor, making it easier for them to enter His Kingdom. Nevertheless, in Romans 2:11 St Paul teaches that “God shows no partiality” and in Galatians 3:28 confirms that “There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus.” How can it be that Jesus gave the poor a preferential option and taught that God made it easier for the poor to enter His Kingdom, while “all are one in Christ Jesus” and while “God shows no partiality”? The answer is, of course, that there is a difference between giving the poor a preferential option and showing favouritism, treating the poor equitably and treating them with what Stephen J Pope calls “unjust partiality.”
As Pope argues, “the preferential option, properly understood, refers to an expansion rather than a contraction of love and wisdom… this form of partiality must not be associated with those forms which encourage a disregard for fairness…” In this way offering the poor a “preferential option” does not take away from the love God – or Christians – shows to others. A parent does not love a child less by choosing to have another child; love is not a finite resource but expands to meet the need. Further, no Christian who proposes giving the poor a preferential option proposes to treat other groups unjustly from now on. Of course there will be those who perceive any measures taken to curtail their unjust privilege as unjust treatment, but is it unjust to stop a thief from enjoying the proceeds of their crimes? As Marx said, capitalism is theft because the capitalist relies on seizing the means of production and paying the workers less than he charges for their labour. Even the father of free-market Capitalism Adam Smith agreed that “It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest.” In this way, the rich are criminals and justice demands that they should not be allowed to enjoy the proceeds of their crimes with impunity. Further, as Rawls pointed out “The principles of justice are chosen behind a veil of ignorance.” Could those who would complain of the injustice of being deprived of unjust privilege say that they would choose for the unjustly privileged to go unchallenged if they did not know that they were so privileged? As Gutierrez pointed out, the poor are in the vast majority, both now and through history. They occupy the underside of history and have suffered in every possible way because of material deprivation. Any theory of justice decided on behind a veil of ignorance could not accept Capitalism, because it is only to the advantage of a tiny and shrinking minority. Further, because Capitalism is structurally sinful it causes even to that minority to be dehumanised and distanced from God, both in this life and the next. Oligarchs and ultra-high-net-worth individuals might appear to benefit from Capitalism – and they certainly enjoy the supercars and mansions – but their property and investments force them to be complicit in the oppression of workers and the destruction of the environment and so ensures that so long as they remain rich, they cannot show agape or follow God’s commandments. By challenging and even by stopping the continuation of a systemic injustice which has so long and so severely oppressed the poor the Christian does not show unjust favouritism, she works for justice – liberating the rich as well as the poor from the structural sin that is capitalism.
In addition, in Luke 6:20 Jesus taught “blessed are the poor”, continuing in verse 24 “woe to you who are rich, for you have already received your comfort.” In this way Christians who commit to giving the poor a preferential option and so prioritizing the poor seem to do only what Jesus said that God would do. Further, even if that is to misinterpret Jesus’ teaching about how God will treat the rich, unlike God whose relationship with the poor and other groups is timeless, the preferential option CELAM called for is time-bound and in response to millennia of injustice and oppression. Where the poor have been given a worse and manifestly unfair option through all recorded human history, addressing this by committing to try to give them a preferential option now is not unfair or unjust. Just as the Black Lives Matter movement draws attention to the value of black lives now and going forward in the context of addressing the effects of centuries of discrimination and oppression, the preferential option for the poor is a step towards – and only a step towards – combating injustice and not in itself a new injustice. In calling for some sort of affirmative action to address injustice, Liberation Theology, Black Liberation Theology and other contextual theologies like feminist and Dalit theologies all draw on the thinking of John Rawls, who pointed out that injustice is done when we treat different groups with different needs differently. He wrote: “The natural distribution is neither just nor unjust; nor is it unjust that persons are born into society at some particular position. These are simply natural facts. What is just and unjust is the way that institutions deal with these facts.” For Rawls, justice demands that institutions focus resources on those who have need, according to their needs, rather than sharing them out equally and giving to those who already have more than they need. This echoes Marx’ mantra “From each according to his ability, to each according to his needs,” a principle that was previously adopted by the Early Church, as described in Acts 4-5. In this way, by prioritizing the poor over wealthier groups, Christians treat all people equitably and so justly rather than equally and so unjustly. To treat all people equally when some are, to quote George Orwell “more equal than others” is actually to prefer the rich and treat the already-privileged with favouritism.
Of course, the title-quote does refer to prioritizing “one group over another” and it is true that this might imply what Pope called “unjust partiality” of the type which takes from one group in order to give to another. If the title is so interpreted then it is fair to say that “Christians should not show favouritism or prioritize one group over another.” St Thomas Aquinas taught that a good judge should not show any favouritism for or discrimination against the poor when passing sentence and indeed, impartiality seems to be a condition of justice. For example, Immanuel Kant taught that a “good will” must “treat humanity, whether in the person of yourself or another, always as an end and never as a means to an end,” suggesting that moral decisions should be made in respect of humanity without consideration of any particular characteristic, protected or otherwise. Nevertheless, Rawls was strongly influenced by Kant and saw no necessary conflict between treating humanity always as an end in itself and demanding that the poor and disadvantaged are prioritized when it comes to resource-allocation. Not giving more to somebody who has enough is not the same as taking from them and so using them as a means to an end of improving conditions for those who lack. It follows that Christians can prioritize the poor by treating them equitably, without acting unjustly with respect of the rich.
Having said that, those who call for a “preferential option for the poor” often call for the abolition of private property in the same breath, and this could reasonably be seen as using property owners as a means and not as an end in themselves. Kant distinguishes between negative and positive duties, arguing that a negative duty – not to do something evil – always trumps a positive duty – to help. So, while not giving more to those who already have enough might be consistent with Kantian Ethics, taking from the rich would not be. This implies that there should be a line for Christians when it comes to giving the poor a preferential option and so prioritizing them and that endorsing the wholesale abolition of private property would cross that line. Nevertheless, Populorum Progressio confirms that for Catholics at least “the right to private property is not absolute and unconditional…” because “The earth belongs to everyone, not to the rich” and “No one may appropriate surplus goods for their own use when others lack the bare necessities of life.” This relates to 1 John 3:17 “But if anyone has the world’s goods and sees his brother in need, yet closes his heart against him, how does God’s love abide in him?” and to Jesus’ own reaction to the Rich Young Man in Mark 10, in asking why – if he has truly followed God’s commandments – he is still rich. While Christians should stop short of supporting Marxist revolutions and a legal abolition of private property, that does not mean that Christians should passively accept the capitalist status quo and its concomitant injustices, including the grossly unequal distribution of private property, a large proportion of which was originally appropriated from what was held in common ownership and more would not have been possible without that appropriation. As CELAM affirmed in “A message to the peoples of Latin America” (1979) and as Jon Sobrino reminds us any “solidarity in faith must of necessity pass through solidarity with the poor.” Christians must choose; even while they should not endorse Marxist revolution, if they want to remain Christians they must divest themselves of their property and stand in solidarity with the poor. Similarly, the Church must now become a “Church of the Poor” as Gutierrez put it, because there is no way for the Church to passively accept its own wealth and privilege because in doing so it implicitly endorses and seems to advocate for injustice. It follows that Christians should prioritize disadvantaged groups such as the poor and while they should not foment violent revolution as a means of abolishing private property, they should set a positive example, both individually and as a Church institution, in divesting themselves of the spoils of Capitalism as the necessary first step on a journey towards a fair and equitable redistribution of resources.
So, in conclusion, Christians should not show favoritism in the sense of displaying what Pope calls unjust partiality, giving to one group by taking from other groups, but they still should – must – prioritize disadvantaged groups and show what Pope calls “just partiality” for them to the extent of sacrificing self to work for justice and their equitable treatment. Jesus’ own example in doing this is one that Christians should follow. Jesus chose to live poor, in solidarity with the poor, and sacrificed himself to change an oppressive, structurally sinful system which benefited nobody in a real and lasting sense. In the same way Christians should accept his challenge to “pick up your cross and follow me,” giving all they have to the poor in the knowledge that – if not in the next life then in this one – this is the only way to build the Kingdom of God.
 Theological Studies, Vol 54, 1993
 Church as Sacrament: Gutiérrez and Sobrino as Interpreters of Lumen Gentium by Todd Walatka, published online by CUP in 2015 https://www.cambridge.org/core/journals/horizons/article/abs/church-as-sacrament-gutierrez-and-sobrino-as-interpreters-of-lumen-gentium/512E3C124F371744588801B105E72C34
 An Inquiry into the Nature & Causes of the Wealth of Nations, Vol 1
 A Theory of Justice
 Towards a Theology of Liberation
 A Theory of Justice
 1875 Critique of the Gotha Program
 ST 2-2, q. 63, a. 4, ad 3
 Jon Sobrino, 1985:37-38