These verses are probably an expression of David"s confidence that the Lord would deliver him in anticipation of that deliverance (cf. Revelation 18:2). The psalmist had already seen the wicked ensnared in their own traps many times, and he was sure this would happen again (cf. Psalm 7:15). [source][source][source]
"Higgaion" is probably a musical notation specifying quieter music. [1][source]