Given that faith requires an obedient, seeking heart, it almost seems
like this is a way to remedy the fall of humankind, and to restore our
obedience to God.
It is true that faith is a requirement to please God.
And without faith it is impossible to please God, because anyone who
comes to him must believe that he exists and that he rewards those who
earnestly seek him. (Hebrews 11:6, NIV)
But it is not true that God demanded faith only after the fall of Adam and Eve.
And the Lord God commanded the man, “You are free to eat from any tree
in the garden; but you must not eat from the tree of the knowledge of
good and evil, for when you eat from it you will certainly die.”
(Genesis 2:16-17, NIV)
The first command given by God was not to eat the fruit from the tree of knowledge. God gave a warning to Adam "when you eat from it you will certainly die". Here God was not only giving a command but demanded trust from Adam. It is like saying "Believe me Adam when I say 'you will certainly die'". Here death was not yet experienced by Adam but I believe that it was well understood by Adam. Allow me to even make a conjecture here that Adam understood the consequence of death that it was separation from God and probably, going to Hell. Here Adam had to have faith in God and the same goes to Eve. I believe that Adam explained very well about the fruit and the punishment to Eve but she failed to have faith in God and believed the words of the serpent who was inferior to her. In other words, Eve had no faith. She was not even putting her faith on the serpent. To put faith on the serpent would mean that even if death actually came over them, the serpent could nullify it's effect. But the serpent did not promise anything to Eve but only said that she will become like God. Eve did not ask the serpent, "OK, if what God said was true, do you have the power to save me from death?". Eve was only curious about what the serpent was saying and wanted to try it, probably, without a second thought. Because Eve failed to have faith, she transgressed, which Adam followed because he loved his wife and now we are all doomed.
Faith was always a requirement from the beginning. Now that Jesus opened the way to God, it is still faith alone that can lead us to God. Without having faith that Jesus is the way to heaven, how can anyone please God. Without believing that Jesus is the Son of God, how can anyone please God who sent Him? If Eve had faith in God, we would not have suffered and Jesus should not have died. Now that Jesus died for us, we need to have faith in Jesus to reconcile with God again.
“Very truly I tell you, whoever hears my word and believes him who
sent me has eternal life and will not be judged but has crossed over
from death to life. (John 5:24, NIV)