John Calvin Commentary Hebrews 10:23

"let us hold fast the confession of our hope that it waver not; for he is faithful that promised:" — Hebrews 10:23 (ASV)

Let us hold fast, etc. As he exhorts here the Jews to persevere, he mentions hope rather than faith; for as hope is born of faith, so it is fed and sustained by it to the last. He also requires profession or confession, for it is not true faith unless it shows itself before others. And he seems indirectly to touch on the pretense of those who, to please their own nation, paid too much attention to the ceremonies of the Law. He therefore urges them not only to believe with the heart, but also to show and to profess how much they honored Christ.

But we should carefully notice the reason which he adds, for he is faithful that promised. For from this we first learn that our faith rests on this foundation: that God is true, that is, true to His promise, which His word contains; for so that we may believe, the voice or word of God must precede; but it is not every kind of word that is capable of producing faith; a promise alone is that on which faith rests. And so from this passage we may learn the mutual relation between the faith of men and the promise of God; for unless God promises, no one can believe.