1 Corinthians 9:2

If I be not an apostle unto others, yet doubtless I am to you: for the seal of mine apostleship are ye in the Lord (KJV)

Then: The proof of Paul's apostleship is the existence of the Corinthian church. Matthew Henry finds a sense of discouragement on Paul's part that he has worked so hard to bring the Corinthians into the body, yet there are so many who question his apostleship, slander his reputation and character. Yet Paul still speaks to them with love.

Now: Henry states that the lack of returning kindness from people where ministers work is common. Wright also refers to poor congregational support of their ministers - either monetary, personal or spiritual. They need to read I Corinthians 9. Even if a minister's reward is the joy of bringing many to eternal salvation, he needs the material, everyday practical necessities of life. He should live at the same standard as his congregation.

Extra source: Commentary on the Whole Bible Acts to Revelation Vol VI by Matthew Henry online at http://www.ccel.org/ccel/henry/mhc6.iCor.x.html