ANSWER: Adam and Eve, very soon after their creation, had an important decision to make that involved a special tree. What was at stake was profound. They had to decide whether they would trust God or trust in their own determination of what they thought was right and wrong. What forced them to decide (a test which God planned) was a tree, in the middle of the Garden of Eden, labeled the knowledge of good and evil (Genesis 2:17). As most people know, our first parents choose unwisely, and thereby bequeathed to humanity an existence of toil and trouble that still exists today.
Eating of the tree of life (Genesis 2:9; 3:22 - 23) symbolized committing to going God's way in faith and obedience, then ultimately be given the gift of living forever. Adam and Eve's eating of the forbidden fruit (Genesis 2:16 - 17; 3:3, 11), however, symbolized man deciding for himself, apart from God, what was right and wrong, good and evil, the best way to live, and so on.As a side note, some wonder what type or kind of fruit was on the tree that symbolized eternal existence. The Bible is unfortunately silent in this regard.
Adam and Eve choose to live life based on their own human reason and emotions, which would ultimately be led by God's adversary Satan the devil (Revelation 12:7 - 9; Isaiah 14:12 - 14; Ezekiel 28:12 - 19). Ironically, they rejected believing in the true God to "worshipping" their own views and opinions. God allowed Man to set himself up as 'god' of the universe created in his own mind in order to learn valuable eternal lessons!
After their sin, God exiled Adam and Eve from the garden and placed a special angel at its entrance to keep the first couple and their descendants from re-entering it. The reason why God did this was to keep them, and all humans, from living forever in misery brought by man's choice to reject him and his ways.
24 Then at the east side of the garden (of Eden) he (God) put living creatures (the NKJV and other translations have 'cherubim,' which are a powerful class of angels like Archangels) and a flaming sword . . . This was to keep anyone (Adam and his descendants) from coming near the tree . . . (Genesis 3:24).
What happened to the tree of life after the sin and banishment of our first parents? It was highly likely destroyed, with the rest of Eden's garden, during the great flood that covered the whole world (Genesis 7:17 - 23). Will we see it sometime in the future? Yes! It is mentioned three times in the Book of Revelation.
Its first mention is when God makes a special promise to those in the church at Ephesus, the very first church to receive a spiritual evaluation by him. Those who overcome will be able to eat from the tree of life (Revelation 2:7)! The second time it is mentioned is in the New Jerusalem God will create and bring down from heaven to the earth (Revelation 22:2). John writes that it will produce each month twelve different fruits! The third and last mention is a statement by God that those who OBEY his commandments (yes, they still are in affect and were never done away with!) will be given the right to eat from it (verse 14)!