An earthen vessel was a common clay cookware item ßfound in 1st–century kitchens. Clay pots were considered of very little value. They broke easily and were inexpensive to replace. While metal and glassware were of great value, a clay pot was not something you would want to present to your guests.
Paul compares himself to an earthen vessel in 2 Corinthians 4:7. His point was that he held very little value compared to the power of God working through him. What is important is the ministry he has been given and the message he bears to the world. Paul doesn’t want to be put on display, as if he or any other servant of God were what is important. Today too the Spirit within us and the Gospel we share deserve priority.
Why a brown paper bag?
The brown paper bag is our modern day translation of an earthen vessel. Cheap, replaceable, and just not that special.