A wonderful image of God’s word:
10. Abraham is asked to entrust himself to this word. Faith understands that something so apparently ephemeral and fleeting as a word, when spoken by the God who is fidelity, becomes absolutely certain and unshakable, guaranteeing the continuity of our journey through history. Faith accepts this word as a solid rock upon which we can build, a straight highway on which we can travel. In the Bible, faith is expressed by the Hebrew word ’emûnāh, derived from the verb ’amān whose root means “to uphold”. The term ’emûnāh can signify both God’s fidelity and man’s faith. The man of faith gains strength by putting himself in the hands of the God who is faithful. Playing on this double meaning of the word — also found in the corresponding terms in Greek (pistós) and Latin (fidelis) — Saint Cyril of Jerusalem praised the dignity of the Christian who receives God’s own name: both are called “faithful”.[Cf. Catechesis V, 1: PG 33, 505A.] As Saint Augustine explains: “Man is faithful when he believes in God and his promises; God is faithful when he grants to man what he has promised”.[In Psal. 32, II, s. I, 9: PL 36, 284.]
Some Hebrew language insight, and a few doctors of the Church.
And the contrast: people are faithful in their belief; God is faithful through acting in our lives. Abraham, of course, is the first person in the Judeo-Christian tradition to experience this mutual relationship, this covenant.