more confused as to why spiritual life couldn't be replaced with physical life
Do you mean...replace physical life with spiritual?
You're here in this life to learn all you can....then back to God you go.
You are an individual as your body can produce nothing else.
The question of this op does make an assumption.
To acquire knowledge of good and evil is sin....
and sin separates Man from God.
Such believe, is why people ask such question.
The question itself indicates a lack of understanding.
The first couple waked with God until they acquired knowledge?...really?
To walk with grace in heaven while not knowing, what is good, and what is evil?
Really?
God separated Himself from Man that we do indeed become individuals.
He's not going to hold your hand.
That comes later.