18:2 my rock. Note the seven-fold metaphor for the power of God in defending His loved ones—rock, fortress, deliverer, strength, buckler, horn, high tower.
18:7 earth shook and trembled. Psalm 18:7-16 give a graphic description of a tremendous convulsion of nature, involving earthquakes, volcanic eruptions, great winds and lightnings, thick darkness, hail stones and deep waters. According to the superscript, David is believed to have written this psalm after the Lord delivered him from the hands of Saul, but no such upheavals took place on these occasions. Commentators usually assume that David was using very picturesque poetic imagery to express his awe and relief when God providentially saved him from Saul’s murderous purposes. The source of this imagery, however, must have been either some real event he had experienced or more likely a vision of some great cataclysm of the past, sent to deliver God’s people from their enemies. The most likely model for David’s figurative narrative would have been the global flood that convulsed the antediluvian world in the days of Noah.
18:16 out of many waters. If this colorful remembrance of the past does reflect the great Deluge, as seems likely, then this concluding verse of the section speaks of Noah being saved from the mighty waters of the Flood as an analogous experience to David’s deliverance from Saul.
18:26 froward. See note on Job 5:13.
18:43 head of the heathen. The latter part of Psalm 18 can be applied literally only to the Messiah, the “anointed” of Psalm 18:50. Only He will be “head of the nations” (note Psalm 2:8) “for evermore” (Psalm 18:50).
18:50 Great deliverance. II Samuel 22 is almost identical to Psalm 18, although “great deliverance” in this final verse is “a tower of salvation” in II Samuel 22:51. See notes on II Samuel 22 for further commentary on the application of Psalm 18:7-16 to the great Flood.