Abraham begat Isaac; and Isaac begat Jacob; and Jacob begat Judah and his brothers;
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Theophylact of Ochrid
Matthew begins the genealogy with Abraham because he was the father of the Hebrews, and because he first received the promises that in his seed all the nations would be blessed (Gen. 22:18). Therefore it is fitting that he should give the genealogy of Christ beginning with Abraham, for the seed of Abraham is Christ by Whom all we nations have been blessed who were formerly cursed. "Abraham" means "father of the nations," and "Isaac," "joy" or "laughter." The evangelist makes no mention of the illegitimate children of Abraham, Ishmael and the others, because the Jews were not descended from them, but from Isaac.
You see that he mentioned Judah and his brothers because the twelve tribes were from them.