What does Psalm 31:18 mean?

In prior verses, David noted that his enemies were whispering plots against him (Psalm 31:13). These were probably physical threats as well as slander and lies. These caused even friends and neighbors to avoid David (Psalm 31:11–12). As part of his prayer for deliverance, David asks for God to silence these enemies (Psalm 31:17). He asks God to turn those deceitful words into silence. He wants his enemies to become like those who cannot speak.

Further, David mentions that his enemies also make arrogant attacks on other godly people. Not only did his foes hate him, but they also despised anyone who was godly. Their evil insults against David and righteous others indicate that they despised the Lord. David associates this kind of hateful speech with "pride and contempt." It is ultimately pride that causes wicked people to oppose the Lord and His people. Such arrogance places them squarely in the Devil's camp. The Devil epitomized pride by seeking to usurp God and place himself on God's throne. He said, "I will ascend above the heights of the clouds; I will make myself like the Most High" (Isaiah 14:14). In response, God will bring the Devil "down to Sheol, to the far reaches of the pit" (Isaiah 14:15).