But we have this treasure in earthen vessels, to show that the transcendent power belongs to God and not to us.
We are afflicted in every way, but not crushed; perplexed, but not driven to despair; persecuted, but not forsaken; struck down, but not destroyed; always carrying in the body the death of Jesus, so that the life of Jesus may also be manifested in our bodies. For while we live we are always being given up to death for Jesus’ sake, so that the life of Jesus may be manifested in our mortal flesh. So death is at work in us, but life in you.
2 Corinthians 4:7–12 (RSV)
A clay jar is an ordinary thing in the first century. Like a used CoolWhip container today, it is for storage of whatever needs to be kept. If it breaks or falls apart, no matter, it is just a clay jar.
Still, a clay jar, or a CoolWhip container, can hold gold bars or precious jewels. It then becomes a thing of great value for what it has within. It becomes the means by which the treasure is kept, protected, and held for proper use.
St. Paul understood that the message of the Risen Christ is the greatest treasure of all time. It is the will and purpose of God that this greatest of all treasures be kept within the clay jars of human beings. It is kept within us for its purpose of being made known to the whole world.
Our Lord has given the Gospel proclamation to the sinners it redeems. The world can see that ordinary people, sinners, have been made new in Christ. Seeing this great wonder of salvation, they hear and trust the Word. They then become the next clay jar to contain and share the Good News.