You have not chosen me. He declares still more clearly that it must not be ascribed to their own merit, but to his grace, that they have arrived at so great an honor; for when he says that he was not chosen by them, it is as if he had said, that whatever they have they did not obtain by their own skill or industry.
Men commonly imagine some kind of concurrence to take place between the grace of God and the will of man; but that contrast, I chose you, I was not chosen by you, claims, exclusively, for Christ alone what is usually divided between Christ and man; as if he had said, that a man is not moved of his own accord to seek Christ, until he has been sought by him.
True, the subject now in hand is not the ordinary election of believers, by which they are adopted to be the children of God, but that special election, by which he set apart his disciples to the office of preaching the Gospel. But if it was by free gift, and not by their own merit, that they were chosen to the apostolic office, much more is it certain that the election, by which, from being the children of wrath and an accursed seed, we become the children of God, is of free grace...
He takes, as the ground of his exhortation, the undeserved favor which he had bestowed on them; for the greater our obligations to the Lord, the more earnest ought we to be in performing the duties which he demands from us; otherwise it will be impossible for us to avoid the charge of base ingratitude.
Hence it appears that there is nothing which ought more powerfully to kindle in us the desire of a holy and religious life, than when we acknowledge that we owe everything to God, and that we have nothing that is our own; that both the commencement of our salvation, and all the parts which follow from it, flow from his undeserved mercy...
That you may bear fruit; for it is hardly possible that any one would devote himself earnestly and diligently to the work, if he did not expect that the labor would bring some advantage. Christ, therefore, declares that their efforts will not be useless or unsuccessful, provided that they are ready to obey and follow when he calls them.
For he not only enjoins on the apostles what their calling involves and demands, but promises to them also prosperity and success, that they may not be cold or indifferent. It is hardly possible to tell how great is the value of this consolation against those numerous temptations which daily befall the ministers of Christ.
Whenever, then, we see that we are losing our pains, let us call to remembrance that Christ will, at length, prevent our exertions from being vain or unproductive; for the chief accomplishment of this promise is at the very time when there is no appearance of fruit.
Scorners, and those whom the world looks upon as wise men, ridicule our attempts as foolish, and tell us that it is in vain for us to attempt to mingle heaven and earth; because the fruit does not yet correspond to our wishes. But since Christ, on the contrary, has promised that the happy result, though concealed for a time, will follow, let us labor diligently in the discharge of our duty amidst the mockeries of the world.
https://www.monergism.com/blog/you-did-not-choose-me-commentary-john-1516