Note 14 at Rom. 5:7: Paul is attempting to explain the great love of God shown to us through grace. He draws on the greatest expression of love known to man, which is laying down your life for another (Jn. 15:13), to illustrate this. However, he goes a step further.

It is possible to imagine someone giving up his life for someone else. That has happened many times. But it is inconceivable that someone would sacrifice his life for his enemy. Yet that is exactly what God did (v. 10). Since that is so, how could we ever doubt God's goodness to us now? On our worst day as a Christian, we love God infinitely more than our best day as an unbeliever.