In the NT both Jesus and Paul treat Abraham as the Bible's best example of a believing man, of a man who lived by faith in God and faith in Christ. Now faith, in its simplest, most elementary sense, is simply the reliance placed by one man in the truthfulness and faithfulness and power of someone else. It is the credit one man places in the word and the capability of another. You see, one trembles at a threat, or obeys a command, or embraces a promises for himself precisely because one accepts to be true what God has said in his Word . Nor is it mere knowledge, such as one might discover by investigation, reasoning, and proof.
Faith is true knowledge, of course, it is the knowledge of the truth.
But faith is the knowledge of truth that we must be told and told by God, otherwise we could not know it. So, when Paul says that Christians live by faith and not by sight, he is simply saying in another way that Christians base their lives, their choices, their actions, their commitments, their hopes, on what God has told them and upon the credit, the reliance they place on his Word. Now this faith is what we see shining so beautifully in Abram's behavior here in Genesis 14. We see it, of course, in the daring with which Abram took off after his nephew and his house when he first learned of Lot's capture. What else was this but Abram remembering that God had given this land to him and to his descendants and that he would be the father of a great nation.