“No eye has seen, no ear has heard, and no mind has imagined what God has prepared for those who love him.”
(1 Corinthians 2:9 NLT)

Grapefruit has a way of changing your facial expression in a hurry. On a 1-10 psychophysical sourness scale it would be rated about an 8. Relative to a sour grapefruit everything else seems sweet. In this life we will experience difficulties that may give us sour feelings but tasting the sourness of earth creates the hope for the sweetness of heaven.