One of the most famous statements we have is about faith—it is the outward sign and the result of the hope we have in Jesus Christ. Sometimes it is the only evidence:
Hebrews 11:1 Now faith is the substance of things hoped for, the evidence of things not seen [from the King James Bible]
You need faith to please God. If you don’t believe in Him, you can’t please Him. And you also have to believe this God wants to reward you:
Hebrews 11:6 And it is impossible to please God without faith. Anyone who wants to come to him must believe that God exists and that he rewards those who sincerely seek him.
This was how Abraham pleased God. He could take Isaac up the mountain to sacrifice him because he believed that God was real and would reward him for his faithfulness:
Hebrews 11:19 Abraham reasoned that if Isaac died, God was able to bring him back to life again. And in a sense, Abraham did receive his son back from the dead.
From this, you could argue that Abraham was making no sacrifice at all because he knew the outcome by faith. Even so, Abraham’s faith was counted to him as righteousness.
The reward isn’t always so immediate. Sometimes, people have to wait for their reward:
Hebrews 11:35-39 … But others were tortured, refusing to turn from God in order to be set free. They placed their hope in a better life after the resurrection. … vs 39 All these people earned a good reputation because of their faith, yet none of them received all that God had promised.