He has made everything appropriate in its time. He has also set eternity in their heart, yet so that man will not find out the work which God has done from the beginning even to the end. [Ecclesiastes 3:11]
This second part of this verse caught my attention when I read the book of Ecclesiastes. The LORD has planted a longing for eternity in the hearts of Mankind. As such since the ancient times, Mankind has been seeking eternal life. Eternity as we know refers to a long indefinite period of time. Our life on earth is definite, even if we live up to 100 years. I am not sure if the ancient ones found the answer, but to me the LORD has given the answer, and that is Jesus. Jesus promises us eternal life.
and I give eternal life to them, and they will never perish; and no one will snatch them out of My hand. [John 10:28]