Leviticus 19:33

If a stranger sojourn - This law to protect and comfort the stranger was at once humane and politic. None is so desolate as the stranger, and none needs the offices of benevolence and charity more: and we may add that he who is not affected by the desolate state of the stranger has neither benevolence nor charity. It was politic to encourage strangers, as in consequence many came, not only to sojourn, but to settle among the Jews, and thus their political strength became increased; and many of these settlers became at least proselytes of the gate if not proselytes of the covenant, and thus got their souls saved. Hence humanity, sound policy, and religion said, Vex not the stranger; thou shalt love him as thyself. The apostle makes use of a strong argument to induce men to hospitality towards strangers: Be not forgetful to entertain strangers, for thereby some have entertained angels unawares, Hebrews 13:2. Moses also uses a powerful motive: Ye were strangers in the land of Egypt. The spirit of the precept here laid down, may be well expressed in our Lord' s words: Do unto all men as ye would they should do unto you.