John Lightfoot on Matthew 15:26

[To the dogs.] By this title the Jews, out of spite and contempt, disgraced the Gentiles, whose first care it was to hate, to mock, and to curse, all beside themselves. The nations of the world [that is, the heathen] are likened to dogs. From the common speech of the nation, rather than from his own sense, our Saviour uses this expression, to whom 'the Gentiles' were not so hateful, and whose custom was to speak with the vulgar.

This ignominious name, like a stone cast at the heathen, at length fell upon their own heads; and that by the hand and justice of God directing it: for although they out of pride and contempt fixed that disgraceful name upon the Gentiles, according to their very just desert, the Holy Spirit recoiled it upon themselves. See Psalm 59:6; Philippians 3:2; Revelation 22:15, &c.