“But we have this treasure in jars of clay, to show that the surpassing power belongs to God and not to us” (2 Cor. 4:7).
Philip Hughes comments:
It is one of the main purposes of this epistle [2 Corinthians] to show that this immense discrepancy between the treasure and the vessel serves simple to attest that human weakness presents no barrier to the purposes of God, indeed, that God’s power is made perfect in weakness (12:9), as the brilliance of a treasure is enhanced and magnified by comparison with a common container in which it is placed.
Source: Philip E. Hughes, Paul’s Second Epistle to the Corinthians (Grand Rapids: Eerdmans, 1973), 135.