It clear that Halakhah requires Jews to behave towards non-Jews in a manner consistent with the Torah’s ethical demands. What’s less clear is the reason for this. The Mishnah writes (Gittin 59a-b):

…One does not restrain poor pagans from collecting the gleanings, forgotton pieces and what is left on the corners of fields mipnei darkhei shalom (on account of the ways of peace).

The Gemara, there (61a), expands, based on a beraita:

One supports poor non-Jews together with poor Israelites, and one visits sick non-Jews together with sick Israelites, and one buries dead non-Jews as one buries dead Israelites mipnei darkhei shalom.

What does “mipnei darkhei shalom” mean? The fact that Hazal (the rabbis) offer it as a reason implies, at least, that a reason is needed. In other words, whatever obligation binds Jews to support the poor and visit the sick of their own communties doesn’t automatically extend to non-Jews. Thus, the additional reason of “mipnei darkhei shalom” is given.

Christian polemicists often pointed to “mipnei darkhei shalom” in order to demonstrate the superiority of Christian universalistic ethics over Jewish particularism. In their view, “mipnei darkhei shalom” is merely a pragmatic concern. Jews should behave a certain way to their non-Jewish neighbors, the argument goes, only to ensure peaceful coexistence.

Many Jewish scholars respond by denying any pragmatic consideration implied by “mipnei darkhei shalom“. Others take more nuanced positions. R. Walter Wurzburger, in Ethics of Responsibility, suggests an approach based on the Rambam in H. Melakhim 10:12 and H. Avadim 9:8 that I think is halakhically and philosophically compelling. The Rambam in Melakhim writes:

The Sages commanded us to visit the sick of the pagans and to bury their dead together with the dead of the Israelites and to support their poor amidst the poor of the Israelites to promote the ways of peace (mipnei darkhei shalom). As it is said: “God is good to all and His compassion extends to all His creatures” (Ps. 145:9). And it is said: “Its ways are the ways of pleasantness and all its paths are peace” (Prov. 3:17).

R. Wurzburger makes the following observation:

In this peroration, Maimonides [Rambam] quotes as prooftext for “the ways of peace” a biblical source that is not mentioned in the Talmud. Why did Maimonides find it necessary to adduce an additional scriptural source, instead of relying exclusively on the biblical passage, “Its ways… are peace,” which, according to the Talmud, serves as the sole biblical basis of “the ways of peace”?

To answer this question, R. Wurzburger directs us to the Rambam in H. Avadim:

With respect to the moral attributes of God that we are commanded to imitate, it is said “and His mercy extends to all.”

Earlier in his work, R. Wurzburger distinguishes between “act-morality” - the familiar action-oriented mitzvot, and “agent-morality” - obligations intended for character development, particularly those relating to imitating divine attributes. He uses this distinction to explain the Rambam here:

Maimonides, apparently, seeks to guard against the misconception that the various laws mandating philanthropy to non-Jews are merely devised to serve Jewish self-interest. He, therefore, cites a biblical verse making it clear that the prescribed practices represent vital components of the religious imperative to engage in imitatio Dei.

By linking the pursuit of “the ways of peace” with the emulation of the divine attribute of compassion, Maimonides suggests that even in situations in which, for technical reasons, certain provisions of act-morality may be inapplicable, considerations of agent-morality form the matrix of additional obligations. Although the Torah’s commandment prescribing alms-giving does not include an obligation to support non-Jewish poor people, agent-morality dictates that we display compassion to all individuals… Whereas Jewish act-morality contains features that differentiate between members and non-members of the Covenantal community, agent-morality makes no distinctions. Insensitivity to the needs of others is no less reprehensible when it is displayed in one’s conduct toward non-Jews than it would be toward Jews.