Geerhardus Vos’ (1862–1949) description of the faith of the Old Testament patriarchs – particularly Abraham – is most excellent. I highly recommend the entire section, but I only have selected a few passages. This section can be found in Vos’ Biblical Theology: Old and New Testaments, p. 83-87.
“Faith was in Abraham’s life the chief religious act and frame of mind. His whole life was a school of faith in which the divine training developed this grace from step to step. Even at the beginning there was a heavy demand on the patriarch’s faith. He was called upon to leave his own country, kindred, father’s house.”
Abraham’s “faith and a desire for more faith” went hand in hand. “There entered into it a personal factor, viz., the trustworthiness of God, who made the declaration of the promises. Religious belief exists not in its last analysis on what we can prove to be so, but on the fact of God having declared it to be so.” “Faith therefore begins and ends in the trust – rest in God.”
“For this treasure [Gen 15.1 – the reward – God himself] he could cheerfully renounce all other gifts.” By faith, “Abraham…renounced all of his own purely human resources. He expected nothing from himself…he expected everything from the supernatural interposition of God…. This is the reason why the Apostle [Paul] compares Abraham’s faith…to the Christian’s faith in the resurrection of Jesus Christ from the dead. This kind of faith is a faith in the creative interposition of God. It trusts in Him for calling the things that are not as though they were…. Abraham learned to possess the promses of God, in the promising God alone. The promises had no chance of becoming materialized through detachment from their centre in God. They could only be had and enjoyed as a part and potential outflow of the divine heart itself. For the promises are like an ethereal garment, more precious than the body of the promised thing over which it is thrown.”
“From the earthly, possessed or not-yet-possessed, they [the patriarchs] had learned to look upward to a form of possession of the promise identifying it more closely with God Himself.”