Romans 4:20-22
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.”
Paul talked about David shortly and then Abraham pretty much the whole chapter. Faith was not only accounted to the apostles in the new testament but also to the great men of the old. Abraham's faith was tested a few times and God has proven him worthy of the calling - becoming the father of all nations.
We knew about our calling fully well when we accepted Jesus Christ as our personal Lord and Saviour, repented, were immersed, committed to service, lived transformed lives, served our fellowmen and shared the Good News to those who needed it. We did all these because of the faith we possessed the moment we found Him.
As Hebrews 11:1 says,
Now faith is the substance of things hoped for, the evidence of things not seen.
By faith, we remain hopeful that He will fulfill His promises in our lives and that someday He will take us and we will all be with Him in His dwelling place forever, just like Abraham.