If you only look at us, you might well miss the brightness. We carry this precious Message around in the unadorned clay pots of our ordinary lives. That's to prevent anyone from confusing God's incomparable power with us.
Treasure is kept in clay jars. In the same way, we have the treasure of the good news in these earthly bodies of ours. That shows that the mighty power of the good news comes from God. It doesn't come from us.