I was recently asked this good question: "Why must we strive for eternal life? Is one lifetime not enough?" I'm glad to see someone thinking rationally about our mortality, because too many people choose to ignore it, thinking and living like they will never die. As for answering the question on why we should strive to live forever after having lived once, I pointed this inquirer to a few things the Lord Jesus has to say about this, and I want to share them here.
First, the choice of whether to live forever or not is not a choice of immortality versus annihilation (not existing anymore). It is a choice between the eternal life of salvation and the eternal death of judgment. Everyone is actually going to live forever whether they want to or not. The question is what state - what destiny - we are going to live in:
The men of Issachar understood the times and knew what Israel
(1 Chronicles 12:32)