4:7, "But we have this treasure in
earthen vessels, that the
excellency of the power may
be of God, and not of us."
Therefore, God has worked something within this old flesh that cannot be seen by other men. Those treasures are buried, and it is our job to work them out. If God has worked them into us by His own free grace, then we should work them out to His praise, honour, and glory. We do these things so that others may see the treasure that is within our earthen vessel. They see these things and glorify our Father as a result. While the working may be difficult, it is still something that we take no credit for, because the excellency of the power is still of God, and never of us.
Also, from the context, it is seen that the preaching of the gospel is a treasure in earthen vessels. While this is the contextual point, all treasures from the Lord can be seen as residing in these clods of clay (earthen vessels) that we have. Preaching is something that cannot be accomplished without the Lord’s help, and He has given His ministers a treasure (talent) that they are to utilize to the comfort and edification of Zion and ultimately to His praise.
Eternally, that treasure would NEVER have resided there had the Lord not done it Himself. However, the working would NEVER have been successful had the Lord not helped us in that endeavor as well. Let us ever work out our own salvation with fear and trembling so that those treasures within us will redound to His glory.