Romans 4:20-22 (NKJV)
He did not waver at the promise of God through unbelief, but was strengthened in faith, giving glory to God, and being fully convinced that what He had promised He was also able to perform. And therefore "it was accounted to him for righteousness."
In chapter four of Romans, Abraham is called the "father of the faithful." Abraham lived long before Moses. All Jews look to Abraham as their father but in doing so they must admit that the Law of Moses cannot be the way to God since Abraham did not have that Law. It is in this sense that a Christian feels a kinship with the Jew because we both claim Abraham as our father, the Jew via physical birth and the gentile via spiritual birth by faith.
This verse helps us to define faith; it is being fully convinced that God is able to keep his promise and acting on that belief. What was the promise God had given to Abraham? It was that he would become the father of a great nation through a son who would be born to he and Sarah, and in him all the families of the earth would be blessed. This verse says Abraham did not waver in unbelief. How did he demonstrate that? When God asked him to offer his son, Isaac as a sacrifice, Abraham immediately began to do this. If he believed God's promise, he had to believe that God was able to raise Isaac from the dead. What a test of faith!
Do you see how this is a glimpse into how another Son who would be sacrificed and would be raised from the dead? It is this kind of faith that is put on our account as righteousness.
1 Corinthians 15:1-4 (NKJV)
... I declare to you the gospel which I preached to you, which also you received and in which you stand, by which also you are saved, ... that Christ died for our sins according to the Scriptures, and that He was buried, and that He rose again the third day according to the Scriptures