Alma 42:5

For behold, if Adam had put forth his hand immediately, and partook of the tree of life, he would have lived forever, according to the word of God, having no space for repentance; yea, and also the word of God would have been void, and the great plan of salvation would have been frustrated.

If Adam had eaten from the tree of life right away, he would have lived forever. He would have had no time to repent. God’s word would have been broken. God’s great plan to save us would have failed.

If Adam had immediately grabbed fruit from the tree of life, he would have lived forever with no opportunity to repent. God’s word would have been broken, and the entire plan of salvation would have fallen apart.