He did not waver in unbelief at God’s promise but was strengthened in his faith and gave glory to God, because he was fully convinced that what He had promised He was also able to perform.
As is written in Hebrews, Abraham knew that Father God was real and trustworthy. Whoever comes to Him must believe that He exists and that He rewards those who seek Him. This is Biblical faith. It existed as long ago as Abraham. By grace he was saved through faith and we can be also.
What else needs to be said?