One of the most fascinating statements Solomon ever made in his book of Ecclesiastes is this one, “He has made everything beautiful in its time. He has also set eternity in the hearts of men; yet they cannot fathom what God has done from beginning to end” (Eccl. 3:11). I believe this is true, and besides the biblical statement, there is evidence in human history to validate the claim.
When I was about seventeen, I read a book entitled Peace Child. In 1962 Don Richardson and his wife, Carol, with their tiny son Stephen arrived in New Guinea to bring the gospel to a cannibal tribe called the Sawi. Richardson made little progress in his attempt to introduce the gospel to these people. In fact, when they heard the gospel story, they admired Judas the betrayer more than Jesus. The reason being is because in their culture the man who could betray his enemy was held in high esteem. Don and Carol threatened to leave if the Sawi did not stop fighting their enemies. The Richardsons watched in total surprise as the two warring tribes reconciled through a “peace child.” The chief's own son would be offered to the other tribe as a “peace child.” It was then that Richardson saw this ritual as a parable of the gospel, in which the Chief of all chiefs made peace with the lost tribe of humanity by offering up his only Son. Many of the Sawi eventually came to know Jesus, and the gospel has spread throughout the region. The whole story of the Sawi and their neighboring tribes is evidence that God has put eternity in our hearts.
Richardson, in another book entitled Eternity in Their Hearts, demonstrates that people from every culture have a deep longing for God. It doesn’t matter whether they were part of an ancient tribe from long ago or part of an urban population of the 21st century, people long to know what’s next.
Richardson writes that God has revealed himself in creation and in oral stories that have been passed down. The Inca king rejected the sun god Inti because he believed there was a greater God who dwells in uncreated light. The Karen people of Burma had legends of a lost book that one day the Supreme God Y'wa would come to set them free from oppression. The people of Borneo had a tribal ritual to make atonement for sin. Every year the Dyaks put their sins on a small boat and sent it down the river with their sins. 
These stories are only a sampling of the fact that God has put eternity in our hearts. We were born with a longing in our hearts to know God, and that longing is for another world—one far different than this one plagued with sickness, injustice and made hopeless by our sins.
C.S. Lewis often wrote about eternity, and he could, I think, write in such eloquent ways, "If I find in myself a desire which no experience in this world can satisfy, the most probable explanation is that I was made for another world. If none of my earthly pleasures satisfy it, that does not prove that the universe is a fraud. Probably earthly pleasures were never meant to satisfy it, but only to arouse it, to suggest the real thing."