1 Corinthians 2:2:

For I decided to know nothing among you except Jesus Christ and him crucified.

Roy Ciampa and Brian Rosner, The First Letter to the Corinthians (Eerdmans, 2010), page 114:

In contrast to “the wise” in Corinth and in the church, who could expatiate endlessly on all sorts of subjects, all Paul wanted to talk about was “the cross of Christ” (1:17). On first blush this may seem rather narrow and limited. After all, Paul spent eighteen months in Corinth and would have engaged in pastoral work alongside evangelism. However, as 1 Corinthians 1:10–4:17 itself demonstrates, for Paul even the most practical ills, such as divisions and problems of leadership in the church, are remedied by focusing on the cross. For Paul, Christ crucified is more than just the means of forgiveness and salvation; rather, it informs his total vision of the Christian life and ministry.