What does Psalm 18:18 mean?

The overall context of these verses is David's rescue from his enemies, for which he credits God's deliverance (2 Samuel 22:1). David's foes confronted him when he felt that his situation was desperate. He confesses that the Lord was his support, so his enemies were unable to kill him. Obviously, David maintained a close, trusting relationship with the Lord throughout his ordeal in the wilderness when a fugitive from Saul, and in other situations against different enemies, and the Lord honored that relationship.

If we depend upon our own wisdom and strength to defeat our enemy, the Devil, we will fail, but if we depend on the Lord for victory, we will enjoy a successful outcome.

We can derive an important lesson on this subject from the life of Samson. When the Spirit of the Lord empowered him, he experienced victory over his enemies. For example, in the power of the Spirit he killed 1,000 Philistines with a donkey's jawbone (Judges 15:15). Soon after the victory, he addressed the Lord and said, "You have granted this great salvation by the hand of your servant" (Judges 15:18).

However, Samson failed to protect his relationship with the Lord. He allowed Delilah, a pagan woman, to deceive him, causing him to place his confidence in himself instead of in the Lord (Judges 16:15–19). When Samson heard the Philistines had gathered in Delilah's home to seize him, he said, "I will go out as at other times and shake myself free," however, "he did not know that the LORD had left him" (Judges 16:20); therefore his enemies captured and humiliated him (Judges 16:21). When we stop depending on God, and start taking pride in our own security, we risk dire consequences.