Romans 4:13 says that it was not through law that Abraham and his offspring received the promise that he would be heir of the world, but through the righteousness that comes by faith.
In the story of Abraham, we are able to see the blessings gleaned from a life of faith. As believers in Christ, we are called to live by faith, trusting in the unseen and hungering for God's will. Faith operates outside the senses (which we as humans rely so strongly upon) - it is that which can't be seen, touched, heard, etc.
Most importantly, we must realize that faith is not an option if we choose to follow Christ; God requires it so that we may act in accordance with his purposes. We must ask God everyday for greater faith and stay grounded in the Word so that we are knowledgeable and emboldened.
God's Covenant with Abraham
In God's covenant with Abraham, he used the words "I will" six times: I will make you a great nation, I will bless you, I will show you a land to dwell in Such wording shows that God was making a promise to Abraham of future things to come.
The results were not instant, but instead required Abraham to walk by faith in order to receive God's blessings. In life, God will never tell us everything, only what is essential for us to know. Not only would complete insight into the mind of God overwhelm our finite and feeble minds, but it would diminish our need to trust Him. Thus, He led Abraham, guiding Him every step of the way through his life of faith, telling him only what was necessary for Abraham's fulfillment of God's plans and for Abraham's future glory.
Abraham, the Father of Many Nations
Three worldwide faiths claim Abraham as their father: Islam through Ishmael (son of Hagar and Abraham), Judaism through Isaac and Jacob (Jacob, or Israel, had 12 sons; all Jews are the descendents of the 12 tribes which arose from the sons), and Christianity through Jesus Christ. Satan loves to cause chaos and confusion, which is exactly why he is so pleased over the spiritual battles between these three faiths.
One interesting fact to ponder: the reason why Muslim terrorists are so vehemently anti-American is because they fear that our culture is poisoning theirs. Muslims live their lives by the Koran (to the point that the Koran dictates law), and they recognize that Americans do not live by the Bible. And it is unfortunately true that in this nation, we are slowly replacing God with immorality. The more that we move away from Him, the more that God will take his hand of protection off of us. We must all turn back (or "cross over" like Abraham did), and live by faith in our Lord God.
Romans 4:20-25 says of Abraham that he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, being fully persuaded that God had power to do what he had promised. This is why it was credited to him as righteousness. The words "it was credited to him" were written not for him alone, but also for us, to whom God will credit righteousness - for us who believe in him who raised Jesus our Lord from the dead. He was delivered over to death for our sins and was raised to life for our justification."