Genesis 2:17 (NKJV)
“but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die.”
This verse presents a huge pothole. Adam did not physically die on the 24 hour day he ate the fruit from the tree of the knowledge of good and evil.
To escape this difficulty, several interpretations have been offered:
1) Adam died spiritually, being separated from God on the 24 hour day that he ate the forbidden fruit. The problem with this "fix" is Genesis 3:19 which imposes the future penalty of physical death.
2) God relented and chose not to impose physical death on the 24 hour day Adam ate the fruit. The problem with this "fix" is when God says "if you do this, I will do that" He only relents when God specifies a conditional, i.e "but if you do this other thing, I will relent.
3) God imposed a specific future event, the penalty of death by imposing mortality. So dying due to mortality, you will die and become dust. I like this one. Thus on the 24 hour day Adam sinned, Adam now being unholy was separated spiritually from our Holy God, and also on the 24 hour day Adam sinned, Adam became mortal so that dying he would die.