Hebrews 10:23

23.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 requires also profession or confession, for it is not true faith except it shows itself before men. And he seems indirectly to touch the dissimulation of those who paid too much attention, in order to please their own nation, to the ceremonies of the Law. He therefore bids them not only to believe with the heart, but also to show and to profess how much they honored Christ.

But we ought carefully to notice the reason which he subjoins, for he is faithful that promised. For we hence first learn, that our faith rests on this foundation, that God is true, that is, true to his promise, which his word contains; for 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 recumbs. And so from this passage we may learn the mutual relation between the faith of men and the promise of God; for except God promises, no one can believe. (176)