The atheist and the shopping trolley

I just received some mail from a very courageous atheist who unfortunately forgot to give his name or address. He (we shall assume my correspondent was male) didn't have anything particularly meaningful to say, but he did include the following joke:

No substitute for penal substitution

The doctrine of penal substitution states that the Lord Jesus Christ bore the judgment of God in the place of sinners so that they can go free. It means that the Christian Gospel is the only message in the world that maintains that God is a righteous God and a Saviour (see for example Isaiah 45 v 21).