Thou, even thou, art terrible. The repetition of the pronoun Thou, is intended to exclude all others from what is here predicated of God, as if it had been said, Whatever power there is in the world, it at once vanishes away, and is reduced to nothing, when He comes forth and manifests himself; and, therefore, He alone is terrible. This is confirmed by the comparison added immediately after, which intimates that, although the wicked are so filled with pride as to be ready to burst with it, yet they are unable to abide the look and presence of God. But as he sometimes keeps silence, and seems merely to look on as an idle spectator, it is expressly asserted, that as soon as he begins to be angry, ruin will be near all the wicked. Although they may then for a time not only stand, but also rise above the clouds by their fury, we are here, notwithstanding, admonished that we ought to wait for the time of wrath. Let us also mark that this terror is denounced against the wicked in such a manner as that it sweetly draws all true believers to God.

Thou, even thou, art to be feared - To be had in reverence or veneration. The repetition of the word "thou" is emphatic, as if the mind paused at the mention of God, and remained in a state of reverence, repeating the thought. The particular "reason" suggested here why God should be had in reverence, was the display of his power in overthrowing by a word the mighty hosts that had come against the holy city.
And who may stand in thy sight - Who can stand before thee? implying that no one had the power to do it. "When once thou art angry." If such armies have been overcome suddenly by thy might, then what power is there which could successfully resist thee?

Thou, even thou, art to be feared - The Hebrew is simple, but very emphatic: אתה נורא אתה attah nora attah, "Thou art terrible; thou art." The repetition of the pronoun deepens the sense.
When once thou art angry? - Literally, From the time thou art angry. In the moment thy wrath is kindled, in that moment judgment is executed. How awful is this consideration! If one hundred and eighty-five thousand men were in one moment destroyed by the wrath of God, canst thou, thou poor, miserable, feeble sinner, resist his will, and turn aside his thunder!

Thou, [even] thou, [art] to be feared: and who may stand in thy (e) sight when once thou art angry?
(e) God with a look is able to destroy all the power and activity of the enemies, no matter how many or mighty.

Thou, even thou, art to be feared,.... By his own people with reverence and godly fear, because of his greatness and goodness; and to be dreaded by his enemies; which seems to be the sense here, as appears by what follows:
and who may stand in thy sight when once thou art angry? or "from the moment thou art angry" (b); so the Targum, from the "time", and Jarchi, from the "hour": that is, as soon as ever his anger begins, when it is kindled but a little, and how much less when it burns in its full strength? there is no standing before his justice, and at his judgment seat, with boldness and confidence, and so as to succeed, or come off acquitted, without having on his righteousness; and much less is there any standing before his wrath and fury, when his hand takes hold on judgment to execute it; see Nahum 1:6.
(b) "ex quo irasceris", Junius & Tremellius, Piscator; "a momento, vel tempore irae tuae", Michaelis.

God's people are the meek of the earth, the quiet in the land, that suffer wrong, but do none. The righteous God seems to keep silence long, yet, sooner or later, he will make judgment to be heard. We live in an angry, provoking world; we often feel much, and are apt to fear more, from the wrath of man. What will not turn to his praise, shall not be suffered to break out. He can set bounds to the wrath of man, as he does to the raging sea; hitherto it shall come, and no further. Let all submit to God. Our prayers and praises, and especially our hearts, are the presents we should bring to the Lord. His name is glorious, and he is the proper object of our fear. He shall cut off the spirit of princes; he shall slip it off easily, as we slip off a flower from the stalk, or a bunch of grapes from the vine; so the word signifies. He can dispirit the most daring: since there is no contending with God, it is our wisdom, as it is our duty, to submit to him. Let us seek his favour as our portion, and commit all our concerns to him.

may . . . sight--contend with Thee (Deuteronomy 9:4; Joshua 7:12).

Nahum also (Psalm 1:6) draws the same inference from the defeat of Sennacherib as the psalmist does in Psalm 76:8. מאז אפּך (cf. Ruth 2:7; Jeremiah 44:18), from the decisive turning-point onwards, from the אז in Psalm 2:5, when Thine anger breaks forth. God sent forth His judiciary word from heaven into the midst of the din of war of the hostile world: immediately (cf. on the sequence of the tenses Psalm 48:6, and on Habakkuk 3:10) it was silenced, the earth was seized with fear, and its tumult was obliged to cease, when, namely, God arose on behalf of His disquieted, suffering people, when He spoke as we read in Isaiah 33:10, and fulfilled the prayer offered in extreme need in Isaiah 33:2.