Matthew 5:43 - Ellicott's Commentary On The Whole Bible

Thou shalt love thy neighbour, and hate thine enemy. — In form the latter clause was a Rabbinic addition to the former; and this is important as showing that our Lord deals throughout not with the Law as such, but with the scribes’ exposition of it. But it can hardly be said these words, as far as national enemies were concerned, were foreign to the spirit of the Law. The Israelites were practically commanded to hate the Canaanites and Amalekites, whom they were commissioned to destroy. The fault of the scribes was that they stereotyped the Law, which was in its nature transitory, and extended it in a wrong direction by making it the plea for indulgence in private enmities. Our Lord cancels the Rabbinic gloss as regards national and, à fortiori, private hatreds, and teaches us to strive after the ideal excellence which He realised, and to love, i.e., to seek the good of those who have shown us the most bitter hostility. So He taught men to find a neighbour even in a Samaritan, and so He prayed, “Father, forgive them, for they know not what they do.”