1 Corinthians 4:15

For though ye have ten thousand instructers in Christ, yet have ye not many fathers: for in Christ Jesus I have begotten you through the gospel (KJV)

Then: When you work your heart out for what you believe in, you cannot step aside and let failure prevail. Paul was their father in Christ. He loved the people he met in Corinth. He wanted them to maintain their position in Christ, not abandon it and slip away into the netherland. Reminding them of his love could counterbalance his previous harsh comments and keep them on track with the Father of the universe.

Now: Paul is slammed as psychologically manipulating the thoughts of the Corinthians (Thiselton, p. 369); however, the tone of the passage indicates a greater sense of concern for his hearers. It would also contradict all that Paul stands for and proves that he is as a follower of Christ. His one and only purpose is to serve the Christ. Undermining his motives seems a useless put down against one who suffered captivity, shipwreck, beatings and death.

Extra source: The First Epistle to the Corinthians: a commentary on the Greek text by Anthony C. Thiselton (Authentic Media, c2000) online at http://books.google.com/books?id=IHG_DNLpmroC&dq=1st+Corinthian+commentaries&printsec=frontcover&source=in&hl=en&ei=W9fQSpC1GILplAfHiumoCg&sa=X&oi=book_result&ct=result&resnum=11&ved=0CB8Q6AEwCg#v=onepage&q=&f=false