What did David mean when he said that the sons of Zeruiah were more severe than him?

The sons of Zeruiah refers to Joab, Asahel, and Abishai (2 Samuel 2:18). They were the children of David’s sister, Zeruiah, (1 Chronicles 2:16) and thus the nephews of David. All of them were eager to shed blood and did not have any reservations in killing fellow Israelites (see 1 Samuel 26:6–8; 2 Samuel 2:18–23). Joab himself did not only kill Abner, but he would later also kill Amasa (2 Samuel 20:4–10) when David sought to give his position to him (2 Samuel 19:13).¹ At this point in time, following the death of Abner, it appears as if David did not have the political strength needed to order the death of Joab and Abishai. This is most likely the sense in which they were too strong for him. They were military leaders in his army and responsible for securing money (see 2 Samuel 3:22).² At present he was thus not able to rebuke them more strongly,³ but on his deathbed he asked his son Solomon to take decisive action (1 Kings 2:5–6, 1 Kings 2:31–34).