Therefore will not we fear - Our confidence in God shall be unshaken and abiding. Having Him for our refuge and strength Psalm 46:1, we can have nothing to fear. Compare Psalm 56:3.
Though the earth be removed - literally, "in the changing of the earth;" that is, though the earth should be changed. This may either mean, Though the earth should change its place or its very structure in these convulsions; or, though it should perish altogether. Compare Psalm 102:26. The idea is, that they would not be afraid, though the convulsions then occurring in the world should be continued, and should be extended so far as to destroy the very earth itself. God would remain their friend and protector, and they would have nothing to fear.
And though the mountains be carried into the midst of the sea - Margin, as in Hebrew, "into the heart of the seas." This may either be understood literally, as implying that they would "not" be afraid though the mountains, the most fixed and firm things of earth, should be uprooted and sunk in the ocean - implying that nothing earthly was stable; or, the mountains here may be referred to as emblems of that which seemed to be most settled and established on earth - the kingdoms of the world. The idea is, that in any convulsion - any change - any threatened danger - they would place confidence in God, who ruled over all, and who could not change. It will be seen at once that this entire description of trust and confidence in God is applicable to the time of Hezekiah, and to the feelings which he manifested when the land was invaded by the hosts of Sennacherib, and when wars and commotions were abroad among the kingdoms of the earth. See the introduction to the psalm. It was, also, eminently suited to console the mind in the circumstances to which Luther so often applied the psalm - the agitations, convulsions, wars, dangers in Europe, in the time of the Reformation. It is suited to any time of trouble, when commotions and revolutions are occurring in the earth, and when everything sacred, true, and valuable seems to be in danger.

Therefore will not we fear - Let what commotions will take place in the earth, we will trust in the all-powerful arm of God. Probably the earthquake referred to, here means political commotions, such as those mentioned under the title; and by mountains, kings or secular states may be intended.

Therefore will not we (c) fear, though the earth be removed, and though the mountains be carried into the midst of the sea;
(c) That is, we will not be overcome with fear.

Therefore will not we fear,...., The consideration of the Lord's being the refuge, strength, and help of his people, in all times of trouble and distress, has a great influence on their faith and confidence, and makes them intrepid and fearless in the midst of the greatest dangers: nor indeed have they any reason to be afraid of men or devils, since the Lord is on their side; nor should they indulge a slavish fear on any account whatever;
though the earth be removed; or "changed" (u), as to its position or fruitfulness; or whatever changes, vicissitudes, and revolutions may be in the kingdoms, nations, and among the inhabitants of the earth, through wars and desolations made thereby;
and though the mountains be carried into the midst of the sea; so the destruction of kingdoms, empires, and cities, is expressed by a like phrase; as of Babylon, Jeremiah 51:25; and of the Roman and Pagan empire, Revelation 6:12, and of the city of Rome, Revelation 8:8.
(u) "cum mutabit", Pagninus; "etiamsi permutarit", Vatalbulus; "si commutaret", Junius & Tremellius, Piscator; so Ainsworth.

The most violent civil commotions are illustrated by the greatest physical commotions.

Though - Though there should be nothing but confusion, and desolations round about us: which are often expressed by such metaphors.