He did not waver at the promise of God through unbelief, but was strengthened in faith, giving glory to God. Romans 4:20
Abraham waited many years for God to keep His promise to bless him with Isaac. Paul writes that Abraham's faith did not weaken. He did not fail to trust God but grew stronger in his faith and continued to give glory to God. Abraham was not a perfect man and made many mistakes in life, but he did not falter in his faith which glorified God. He believed that the God who spoke to Him would do exactly what He promised even after years passed without that promise being fulfilled.
There are many promises of God, and it is only by faith we need to trust His Word and believe His promises. It is hard but let none of us weaken our faith at the Lord's promises through His word because the Word says that what God said He will carry out to completion. Abraham’s life is the perfect example of how important it is to trust God, for without faith it is impossible to please God. Our God is faithful and trustworthy, and all His promises are 'Yes' and 'Amen' in Christ Jesus.