What does Psalm 55:18 mean?

Clues in this psalm suggest David was writing in response to the rebellion of his son, Absalom (Psalm 55:2–8; 2 Samuel 15:14). This coup was assisted by David's former ally, Ahithophel (Psalm 55:12–13; 2 Samuel 15:31). During this incident, David was forced to flee so his family would not be killed by those aligned with Absalom. This verse mentions a large number collected against David, as is mentioned in Psalm 3, specifically referring to the rebellion of Absalom (Psalm 3:1). Of course, that was not the only time when David faced an enemy with greater numbers or power (1 Samuel 17:4, 48; 19:18; 21:10; 23:14).

Here, David suggests that his safety is ensured, despite the size of his enemy. God had previously promised to protect David's throne (2 Samuel 7:9, 11). Though David faces many adversaries, he is supremely confident that the Lord will not let him fall (Psalm 55:16).

The word "redeem" in this verse is from the Hebrew root word padah, which can also mean to deliver or to rescue. David was confident the Lord would fight for him. The apostle Paul encourages Christians to rest assured that no enemy can stand against them. He writes, "If God is for us, who can be against us?" (Romans 8:31). In verse 37 he exclaims, "We are more than conquerors through him who loved us." He follows this exclamation with a list of calamities that might assail the believer, but he affirms that none of these things "will be able to separate us from the love of God in Christ Jesus our Lord" (Romans 8:39).