He is sure that in heaven there are no tears. What he sings is that he knows there'll be no more tears in heaven. Tears are for the earth. Tears are grief's constant companion. Tears are grief's way of showing us the pit of emptiness that tugs so heavily upon us in our time of loss.
Tears are important for the grieving process.
Just when we think we've put our grief behind us, the tears well up and remind us again of our loss. Tears are good. Tears are an important part of the healing process. Listen to the brief verse of Clapton's song which sings of hope. He moves from this verse, however, right back to a repeat of verse one.