What does 1 Kings 2:8 mean?

And remember Shimei son of Gera, the Benjamite from Bahurim. He cursed me terribly when I went to Mahanaim. But when he came down to meet me at the Jordan, I swore by the Lord I wouldn't kill him. 1 Kings 2:8 - Modern Text Bible

(David recalls how Shimei insulted him, but David spared his life with an oath.)