[Though] the waters thereof roar [and] be troubled,.... The noise of which causes men's hearts to fail them for fear, Lu 21:25;[though] the mountains shake with the swelling thereof. All these figurative expressions denote the hurlyburlies, confusions, and disorders that have been or will be in the world; amidst all which the people of God have no reason to fear; for it is always well with the righteous, let it go how it will with others.
The passage may be applied to the destruction of Jerusalem, and the wars preceding it, and the dispersion of the Jews upon it; when true believers in Christ found him to be their refuge, strength, and help in that time of trouble, such as never was the like, and were safe and without fear; and Aben Ezra, a Jewish commentator, thinks it is right to interpret this psalm concerning the wars of Jerusalem: moreover, these words may be applied to any other time of calamity, through war or persecution, that has been since; as also to any that is to come; as to the slaying of the witnesses, the hour of temptation that will try all that are upon the earth; and even to the day of judgment, when heaven and earth shall flee away from the face of the Judge; when the heavens shall be folded up as a garment, and the earth, and all that is therein, shall be burnt up, and the whole world of the ungodly shall be thrown into the utmost panic, the saints will be safe with Christ, and ever happy with him; and, in the worst of times in this world, God is always their covenant God, their shield, portion, and exceeding great reward; Christ is their Redeemer and Saviour, their city of refuge, and strong hold; and though they may be plundered of their goods and property, they have a better and a more enduring substance in heaven; an estate, an inheritance there, that can never be taken away; and even should their enemies kill the body, that is the utmost they can do; their souls are safe in the hands of Christ; their life is hid with him; and when he shall appear, they shall appear with him in glory; and therefore they may well say, "we will not fear" .
Selah; on this word, See Gill on "Ps 3:2". "Si fractus illabatur orbis", &c. Horat. Carmin. l. 3. Ode. 3. v.