The Apostle Peter
1 Peter 1:21BSB·traditional attribution

Through Him you believe in God, who raised Him from the dead and glorified Him; and so your faith and hope are in God.

John Calvin Reformed @genevareformer

21 Who believe The manifestation of Christ refers not to all indiscriminately, but belongs to those only on whom he by the Gospel shines. But we must notice the words, Who by him believe in God: here is shortly expressed what faith is. For, since God is incomprehensible, faith could never reach to him, except it had an immediate regard to Christ.

Matthew Henry Presbyterian @wholebiblehenry

Here the apostle begins his exhortations to those whose glorious state he had before described, thereby instructing us that Christianity is a doctrine according to godliness, designed to make us not only wiser, but better. I. He exhorts them to sobriety and holiness. 1. Wherefore gird up the loins of your mind, etc., Pe1 1:13.

Commenting on 1 Peter 1:13-23

John Gill Reformed Baptist @doctorgill

Who by him do believe in God,.... Christ, as God, is the object of faith; as Mediator, he is the way to the Father, by which men come to him, believe in him and lay hold upon him, as their covenant God and Father; and is also the author of that faith by which they believe in him; and all their encouragement to believe is...