2 Corinthians 3:6

3:6 who made us adequate to be servants of a new covenant not based on the letter but on the Spirit, for the letter kills, but the Spirit gives life.

2 Corinthians 7:8

7:8 For even if I made you sad by my letter, I do not regret having written it (even though I did regret it, for I see that my letter made you sad, though only for a short time).