Paul refers to an earlier "letter of tears" in 2 Corinthians 2:3-4 and 7:8. 1 Corinthians does not match that description; so this "letter of tears" must be between 1 Corinthians and 2 Corinthians.
The abrupt change of tone from being previously harmonious to bitterly reproachful in 2 Corinthians 10-13 has led many to speculate that chapters 10-13 form part of the "letter of tears" which were in some way tagged on to Paul's main letter. Those who disagree with this assessment usually say that the "letter of tears" is no longer extant.
Some scholars also find fragments of the "warning letter", or of other letters, in chapters 1-9, for instance that part of the "warning letter" is preserved in 2 Cor 6:14-7:1, but these hypotheses are less popular.
Paul's contacts with the Corinthian church can be reconstructed as follows:
Paul visits Corinth for the first time, spending about 18 months there (Acts 18:11). He then leaves Corinth and spends about 3 years in Ephesus (Acts 19:8, 19:10, 20:31). (Roughly from AD 53 to 57, see 1 Corinthians article).
Paul writes the "warning letter", probably from Ephesus.
Paul visits the Corinthian church a second time, as he indicated he would in 1 Corinthians 16:6. This is probably still during his 3 years based in Ephesus. 2 Corinthians 2:1 calls this a "painful visit".
Paul writes the "letter of tears".
Paul writes 2 Corinthians, indicating his desire to visit the Corinthian church a third time (2 Cor 12:14, 2 Cor 13:1). The letter doesn't indicate where he is writing from, but it is usually dated after Paul left Ephesus for Macedonia (Acts 20), from either Philippi or Thessalonica in Macedonia.
Paul presumably made the third visit after writing 2 Corinthians, because Acts 20:2-3 indicates he spent 3 months in Greece. In his letter to Rome, written at this time, he sent salutations from some of the principal members of the church to the Romans.
1:12 - 7:16 - Paul defends his actions and apostleship, affirming his affection for the Corinthians.
8:1 - 9:15 - Instructions for the collection for the poor in the Jerusalem church.
10:1 - 13:10 - A polemic defense of his apostleship
13:11-14 - Closing greetings
In Paul's second letter to the Corinthians he again refers to himself as an apostle of ChristJesus by the will of God and reassures the people of Corinth will not have another painful visit but what he has to say is not to cause pain but to reassure them the love he has for them. It was shorter in length in comparison to the first and a little confusing if the reader is unaware of the social, religious, and economic situation of the community. Paul felt the situation in Corinth was still complicated and felt attacked. Some challenged his authority as an apostle and compares the level of difficulty to other cities he has visited who had embraced it, like the Galatians. He is criticized for the way he speaks and writes and finds it just to defend himself with some of his important teachings. He states the importance of forgiving others, and God's new agreement that comes from the Spirit of the living God (2 Cor. 3:3), and the importance of being a person of Christ and giving generously to God's people in Jerusalem, and ends with his own experience of how God changed his life (Sandmel, 1979).
This epistle, it has been well said, shows the individuality of the apostle more than any other. "Human weakness, spiritual strength, the deepest tenderness of affection, wounded feeling, sternness, irony, rebuke, impassioned self-vindication, humility, a just self-respect, zeal for the welfare of the weak and suffering, as well as for the progress of the church of Christ and for the spiritual advancement of its members, are all displayed in turn in the course of his appeal."--Lias, Second Corinthians.