by John Piper, from his book "When I Don't Desire God", page 33-34
"God defines evil this way when he says, “My people have committed two evils: they have forsaken me, the fountain of living waters, and hewed out cisterns for themselves, broken cisterns that can hold no water” (Jer. 2:13). God pictures himself as a mountain spring of clean, cool, life-giving water. The way to glorify a fountain like this is to enjoy the water, and praise the water, and keep coming back to the water, and point other people to the water, and get strength for love from the water, and never, never, never prefer any drink in the world over this water. That makes the spring look valuable. That is how we glorify God, the fountain of living water.
But in Jeremiah’s day people tasted the fountain of God’s grace and did not like it. So they gave their energies to finding better water, more satisfying water. Not only did God call this effort futile (“broken cisterns that can hold no water”), but he called it evil: “My people have committed two evils.” They put God’s perfections to the tongue of their souls and disliked what they tasted; then they turned and craved the suicidal cisterns of the world. That double insult to God is the essence of what evil is.
So preferring the pleasures of money or power or fame or sex over the “pleasures . . . at [God’s] right hand” (Ps. 16:11) is not like preferring caramel to hot fudge. It is a great evil. Indeed it is the ultimate meaning of evil. Esteeming God less than anything is the essence of evil."