Well, basically he wrote to correct sinful practices and refute false doctrines, of the fledgling church in Corinth. He was writing in response to a letter sent to him (7:1) asking for his advice. (Members of “Chloe’s household” also had kept him appraised. (1:11)).
His main goal was that the Corinthian church would be united in Christian love. “Now I plead with you, brethren, by the name of our Lord Jesus Christ, that you all speak the same thing, and that there be no divisions among you, but that you be perfectly joined together in the same mind, and in the same judgment.” (1:10) This was his goal; but the reality was, there was already all sorts of controversies and divisions among them. These had been reported back to him, so he’s now writing to address those issues.
Paul himself was right at the middle of one of the chief controversies. It had been reported to him that the brethren were all lining up behind specific leaders and teachers, and being contentious with each other, “’I am of Paul,;’ or ‘I am of Apollos’ or ‘I am of Cephas,’ or ‘I am of Christ.’” (1:12) Paul asks them, “IS Christ divided? Was Paul crucified for you? Or were you baptized in the name of Paul?”
Another issue splitting up the community was sexual immorality. Corinth was a trade center and as a result had a population of transient people had quite an immoral environment. Like most ancient port cities, it had a reputation for its wildness. In the case of the Corinthian church, Paul cites some examples, specifically incest. He comes right out and says, they must not keep company with an immoral brother, but need to toss him out of the community. (5:11).
Another issue he was addressing was the fact that the believers in Corinth were suing each other. St. Paul claims that, “It is an utter failure for you that you go to law against one another.” (6:7) The saints will judge the angels, yet they want to take their affairs and have them judged outside the Church?
He addresses many other issues, but the unity of the Church is at the heart of each. Other issues include, “food offered to idols (chp 8-10),” Christian marriage (chp. 7), women praying and prophesying with heads uncovered (chp.11), the use of spiritual gifts (chp. 12-14), and the resurrection (chp.15). But St. Paul is certain all these issues that divide them, can be overcome with love. In his closing paragraph, he uses the word twice: “Let all you do, be done with love.” (16:14) and, “If anyone does not love the Lord Jesus Christ, let him be accursed.” (16:22) He wrote to them to encourage them to overcome division, with love.