The “I” of Isaiah 50 - the Servant of Yahweh, or the prophet himself - expects to be justified (v. 8; verb is matzdiqi from tzadaq ). How will he be justified?
He will be justified because Yahweh has given him a tongue to “hasten” the weary, to urge them on, and because Yahweh has awakened and opened his ear, once dead and buried. He doesn’t rebel, doesn’t turn back (vv. 4-5). With his ear opened to Yahweh, he presses forward, following the path of obedience and yielding his back, beard, and face to beatings, humiliation, insults (v. 6). His face full of flinty determination, knowing that he will not be ashamed, he moves ahead (v. 7). For that reason, he is justified (v. 8).
Justification in this text doesn’t come at the beginning but at the end. And it is the obedient one, the servant with the open ear who is justified.