The First Epistle to the Corinthians was a letter authentically written by Paul the Apostle in the mid-1st century (CE) to address problems that had arisen in the Christian congregation at Corinth.
While it is the consensus among scholars that Paul did author this epistle around 54 CE, some scholars believe that Sosthenes, mentioned in the letter's incipit, was a scribe who write for Paul, although Paul states near the end that he wrote the greetings to the Corinthians himself.
Paul wrote to the Corinthian church for a number of reasons. He realizes the church at Corinth is divided and explains that although himself and a few disciples had helped start the church, the church was really headed by Christ Jesus Himself. "I planted the seed, Apollos watered it, but God has been making it grow." (TNIV)
Paul scolds the church members there for sexual immorality and asks for these immoral people to be thrown out of the church.
He gives instructions for marriage, against worshipping worthless idols (idolatry), for spiritual gifts like prophecy. Paul praises the superior way of love and urges the church to be united.
At the end, Paul states that the resurrection of Christ is true. He supports it with testimonies from "more than five hundred of the brothers and sisters" and it is this very truth which makes certain the believers will have eternal life.
Finally Paul tells of his plans to visit the Corinthians, and that Timothy, his co-worker, is coming to their church very soon.