Romans 4:20-21 - Yet he (Abraham) 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.
Abraham is referred to as the father of faith. He gained this title, not because he was perfect or did everything right, but because when God made him a promise he believed it. Abraham and his wife, Sarah, had hoped and prayed for a child all their lives, but they were getting old. They were both past normal child bearing age, but God made a promise to Abraham. He told him that his offspring would be too many to count and that he would be the father of many nations.
In the natural this was hard to see, but Abraham believed God. And according to the promise they had a child. This child was the fulfillment of what God had told him. Then soon after God asked Abraham to offer up his boy as a sacrifice to Him. Instead of complaining and making excuses Abraham was willing to do this.
See, God had promised Abraham offspring through his son Isaac, and Abraham knew that God always stayed true to His promises. No matter what happened, Abraham knew God would deliver Isaac back to him. As the story continues we see that is just what God did. There was a ram provided as a substitute and Isaac was given back to his father.
In this verse Paul describes the faith of Abraham. He tells us that “he did not waver through unbelief” and that he was “fully persuaded that God had power to do what He had promised.”
Faith is looking at what seems to be real and saying we are going to believe God instead. We are not to be moved by what we see, but by the Word of God and His Spirit inside of us. Circumstance may try and tell you one thing, but instead, let God’s Word “fully persuade” you to believe all that He has promised. His Word is true and His promises will be fulfilled.