If we are granted entrance into Heaven through faith in the living God, what about Adam and Eve? They had knowledge but not faith. Will we be able to see them in Heaven?
The first assumption to correct is that entrance into heaven is by faith in the promises of God. We have faith in what God tells us even though we cannot see it.
Hebrews 11:1 tells us:
Now faith is the assurance of things hoped for, the conviction of things not seen.
The object of our faith has changed over history as God has revealed more to us in His word. Today we understand His plan was fulfilled in Christ. So we have faith in the promise that Christ's death paid the price for our sin, and as He was resurrected, we will be also. We cannot see this yet, but we hold the conviction and the hope as if it was true already.
But what about for those who lived before Jesus was revealed as our Messiah? What was revealed to Adam and woman determined whether they showed faith or not, namely after they fell into sin where they redeemed or not?
We get our evidence from Genesis Chapter 3, when God pronounced consequence for their sin. Yet God promises that through woman’s seed (the line of humanity that would come from her) there would be redemption - specifically a Messiah to be born through her line. That Messiah would then have enmity with Satan.
At the time of God’s promise, the female is called Woman (meaning “of man”). The fact that Adam renames his wife from Woman to Eve (“mother of living”) is proof he believed in the promises God just spoke. As such Adam (and Eve) was saved by this faith.
