David does not fear the armies of the enemy; their wickedness is the primary weapon. David stands secure in God's presence, for their own treachery is their downfall.
His guide is his heart which still calls out to God. He desires to be in the House of the Lord. In it he finds shelter and security. Several references to slander and verbal assault are mentioned, and David finds strength in music, the words reassure him and the melody recalls the Lord's presence.
He closes with a final benediction to cheer the heart of a fearful companion: be strong and take heart and wait for the Lord.
In verse 3 he brings the "voice of the Lord" into our notice. I guess I think of thunder as one evidence of God's voice. I know the scientific definition of thunder excludes God's activity, but this is a personal thing.
Cedars of Lebanon were prized in the ancient world for buildings and boats. They were imported to Egypt and planted there as a resource for future building before 1100 bce.
Sirion in vs. 6 is Mount Hermon. All the metaphors emphasize the power and majesty of God. Read it and remember where he is powerful in your own life.