I am become a stranger unto my brethren - That is, They treat me as they would a stranger; as one in whom they have no interest, and whom they regard with no friendship. Compare the notes at Psalm 31:11.
And an alien unto my mother's children - A foreigner; one of another tribe or nation; one to whom they were bound by no tie of relationship. The allusion in the language "unto my mother's children" is intended to denote the most intimate relationship. In families where a man had many wives, as was common among the Hebrews, the nearest relationship would be denoted by being of the same "mother" rather than of the same "father." See the notes at Psalm 50:20. The same thing occurs also where polygamy is not practiced, in cases where a man has married more wives than one. The idea of the psalmist here, therefore, is, that his nearest relatives treated him as if he were a stranger and a foreigner. Compare Job 19:13-19.

I am become a stranger unto my brethren,.... Not only to the Jews in general, who were his own people and nation, to whom he came, and of whom he came; who received him not, hid as it were their faces from him, and rejected him as the Messiah; but also to such who were still nearer akin to him, according to the flesh, who did not believe in him, John 7:5; and even in some sense to his disciples and followers; some of which having heard some doctrines delivered by him not agreeable to them, withdrew from him, and walked no more with him, John 6:60; yea, to his apostles, whom he often called his brethren: one of these betrayed him, another denied him with oaths and cursing, and all of them forsook him and fled, when he was taken by his enemies, and about to suffer death;
and an alien unto my mother's children; which is the same as before, in other words. The Targum is,
"as the son of the Gentiles to my mother's children;''
that is, as an Heathen to them; see Matthew 18:17.