and 8. They break forth into singing. Here he shows how greatly tyrants are hated by the whole world. When they are dead or ruined, all men break forth into joy, and express the feelings which they formerly entertained towards the tyrants, and which they dissembled through fear. Then do their hatred and spite burst forth, and not only do men make known their joy, but even the dumb creatures, as the Prophet, for the sake of amplification, adds the fir-trees and the cedars. As tyranny overturns everything, so when tyranny is done away, everything appears to be restored to its original condition. Since thou art laid down, no feller is come up against us. To make the discourse more energetic, he adds a personification, in which he introduces the trees as speaking and congratulating themselves that, since the tyrant is dead, they will now stand gladly and at ease. The design of the Prophet is to show, that the Heavenly Judge cannot endure tyrants, who are abhorred by the whole world. Hence, we ought to conclude that, though under the sway of tyrants unhappy men are silent, and do not venture to open their mouths, yet the Lord listens to their secret groans. Let us not wonder therefore that tyrants come to such a dismal end; for God, who is a witness of the injuries which they have inflicted, must in the exercise of his justice assist the innocent.

The whole earth is at rest - The kingdom of Babylonia, or Chaldea, extended nearly over the whole pagan world. Now that Babylon was fallen, and that those oppressions would cease, the world is represented as in peace and quietness.
They break forth into singing - That is, the inhabitants of all the nations that were subject to Babylon now rejoice that they are released from its galling and oppressive yoke.

The whole earth is at (e) rest, [and] is quiet: they break forth into singing.
(e) Meaning that where tyrants reign, there can be no rest or quietness and also how detestable a thing tyranny is, seeing the insensible creatures have opportunity to rejoice at their destruction.

The whole earth is at rest, and is quiet,.... The troubler of them being gone; and which will be the ease of the people of God, who in the latter day will fill the face of the earth, when the beast and false prophet will be taken and cast alive into the lake of fire; and especially when Satan shall be bound, and put in prison for a thousand years, that he may deceive the nations no more, Revelation 19:20,
they break forth into singing; that is, the inhabitants of the earth, because of the fall of the king of Babylon, they being delivered from so great a tyrant or oppressor; or, "utter a song of praise", as the Targum, Aben Ezra says the word in the Arabic language is expressive of "clearness", and so it does signify to speak purely, dearly, and fluently, with open, mouth, and a clear voice (z); it is rendered in Psalm 98:4 "make a loud noise"; by singing a joyful song; and such a song will be sung by the church, when the mystical Babylon is fallen; see Revelation 15:2.
(z) "perspicuo, puriore sermone fuit, fluida oratione disertas fuit, ----diserte, eleganter locutus est", Castel. col. 3040.

they--the once subject nations of the whole earth. HOUBIGANT places the stop after "fir trees" (Isaiah 14:8), "The very fir trees break forth," &c. But the parallelism is better in English Version.

"The whole earth rests, is quiet: they break forth into singing. Even the cypresses rejoice at thee, the cedars of Lebanon: 'Since thou hast gone to sleep, no one will come up to lay the axe upon us.'" The preterites indicate inchoatively the circumstances into which the whole earth has now entered. The omission of the subject in the case of pâtz'chu (they break forth) gives the greatest generality to the jubilant utterances: pâtzach rinnâh (erumpere gaudio) is an expression that is characteristic of Isaiah alone (e.g., Isaiah 44:23; Isaiah 49:13); and it is a distinctive peculiarity of the prophet to bring in the trees of the forest, as living and speaking beings, to share in the universal joy (cf., Isaiah 55:12). Jerome supposes the trees to be figuratively employed here for the "chiefs of the nations" (principes gentium). But this disposition to allegorize not only destroys the reality of the contents, but the spirit of the poetry also. Cypresses and cedars rejoice because of the treatment which they received from the Chaldean, who made use of the almost imperishable wood of both of them for ornamental buildings, for his siege apparatus, and for his fleets, and even for ordinary ships - as Alexander, for example, built himself a fleet of cypress-wood, and the Syrian vessels had masts of cedar. Of the old cedars of Lebanon, there are hardly thirty left in the principle spot where they formerly grew. Gardner Wilkinson (1843) and Hooker the botanist (1860) estimated the whole number at about four hundred; and according to the conclusion which the latter drew from the number of concentric rings and other signs, not one of them is more than about five hundred years old.
(Note: See Wilkinson's paper in the Athenaeum (London, Noverse 1862).)

The earth - The subjects of that vast empire, who groaned under their cruel bondage.