Ironically, Solomon speaks of eternity in our hearts in a passage about time. Merriam-Webster defines eternity as infinite time or a seemingly endless or immeasurable time. God created humankind in his image, which is eternal. As a result, we are concerned about the future and desire to understand the beginning from the end. We have a sense there is something that transcends our situation.
Created to be Different
Humans are the only worshipping animal. Evolution can’t explain this quality. If you look at a well-fed dog in front of a fire on a cold day, he is satisfied. If we take a person and put them in the same position, soon they will feel a sense of restlessness. We search for what is beyond what we can feel or sense.
St Augustine prayed, “Thou has made us for Thyself, and our hearts are restless until we learn to rest in Thee.”
God designed our hearts with a hole that can only be filled with Him. This explains why no one, including Solomon, can be satisfied with their accomplishments. Only when we allow God to enter our hearts and place His plan and purpose there can this restlessness be satisfied.
Redeemed for Eternity
God did create us in His image, but sin corrupted this. Romans 3: 23 For everyone has sinned; we all fall short of God’s glorious standard.  This eternity in our heart or God consciousness is still part of our nature, although sin suppresses it. Romans 1: 18 But God shows his anger from heaven against all sinful, wicked people who suppress the truth by their wickedness. 19 They know the truth about God because he has made it obvious to them. 20 For ever since the world was created, people have seen the earth and sky. Through everything God made, they can clearly see his invisible qualities—his eternal power and divine nature. So they have no excuse for not knowing God.
But through His love, God sent His Son, Jesus, to redeem and restore us. Romans 3: 24 Yet God, in his grace, freely makes us right in his sight. He did this through Christ Jesus when he freed us from the penalty for our sins. 25 For God presented Jesus as the sacrifice for sin. People are made right with God when they believe that Jesus sacrificed his life, shedding his blood.
As we believe and trust Jesus, we have the promise of eternity with Him. 1 John 2: 24 So you must remain faithful to what you have been taught from the beginning. If you do, you will remain in fellowship with the Son and with the Father. 25 And in this fellowship we enjoy the eternal life he promised us.
To learn more about eternity in our hearts, listen here:
 Stedman, Ray, 1999, Is This Alll There is to Life, Discovery House Publishers, Grand Rapids, MI, p.51.
[3-6] Holy Bible, New Living Translation, copyright © 1996, 2004, 2015 Tyndale House Publishers, Inc., Carol Stream, Illinois 60188.