And there is also with you Shimei the son of Gera, the Benjaminite from Bahurim, who cursed me with a grievous curse on the day when I went to Mahanaim. But when he came down to meet me at the Jordan, I swore to him by the LORD, saying, ‘I will not put you to death with the sword.’
Shimei cursed David grievously when he fled Absalom, then humbled himself at Jordan and received a sworn pardon. But David's oath did not bind Solomon; an oath made under duress to one man cannot fetter his successor, especially if that man commits fresh offence.
AI summary
David swore to spare Shimei, yes, but warned Solomon against him as turbulent and dangerous to the state. This is not vindictiveness; it is a king and magistrate noting crimes he could not punish, pointing out those whom Solomon must remove for safety of the realm.
AI summary
Thou hast with thee Shimei - See on Sa2 16:5 (note), etc., and the notes on Sa2 19:18-23 (note).