What does Psalm 18:23 mean?

In the context of a person's life, the term "blameless" does not imply absolute perfection. The concept involves a person not leaving any room for others to criticize their behavior. In this passage of Scripture, David praises God for rescuing him from his enemies. David partly credits that deliverance to his obedience to God's commands (Psalm 18:22). Especially in his early life, David's commitment to the Lord's will was tremendous (1 Samuel 13:14). He led an upright life because he wanted to do what was right in the Lord's eyes. He practiced self-discipline. No sin overwhelmed him or even caused him to slip from the path of righteousness. Later in life, some of David's choices would be tragic (1 Kings 15:5), yet the overall pattern of his life was to honor God.

Proof of David's uprightness and self-discipline includes his kind treatment of Saul. Saul, the prior king of Israel, persecuted David and tried to have him murdered. At one point, Saul entered the very cave where David and his men were hiding, and David's men suggested this was the chance to assassinate their enemy. Instead, David "arose and stealthily cut off a corner of Saul's robe" (1 Samuel 24:4). He explained to his men, "The LORD forbid that I should do this thing to my lord, the LORD's anointed, to put out my hand against him, seeing he is the LORD's anointed" (1 Samuel 24:6).

David's men were ready to attack Saul, but David would not permit them to do so (1 Samuel 24:7). Instead, David demonstrated his mercy in an effort to soften Saul's hatred (1 Samuel 24:8–11). Later David had another opportunity to kill Saul and again refused to do so, again stating that it was not for him to kill the LORD's anointed. Instead, David trusted that God Himself would strike Saul or that Saul would die in battle (see 1 Samuel 26).