What does it mean to cut Rahab in pieces in Isaiah 51:9?

These verses have unfolded before our minds a glorious and desirable prospect, only to be realized when the Lord Jesus comes again. Hence the call of verse 9: "Awake, awake, put on strength, O Arm of the Lord." In prophetic vision John saw Him so doing, in Revelation 19:11-16, when He will be displayed as King of kings and Lord of lords. The Lord Jesus has ever been the Executor of the purposes of God. He acted in the mighty scenes of creation. It was He who cut in pieces Rahab — a name meaning "Arrogance," given to Egypt in contempt — and dried up the sea, when God brought the people under Moses out of the land of their bondage. When He puts on strength and acts in the future day, there will be a far greater deliverance, and the ransomed of the Lord shall return to Zion with singing, and their joy will be everlasting and not transient and fleeting as all joyful deliverances have been hitherto in this sinful world. We today may call upon the Arm of the Lord to awake, only the language we use is, "Even so, Come, Lord Jesus."

Similarly the Spirit now answers, as it were, in the remnant. First, they call for the power of Jehovah to assert itself against their mighty foes, as of old against proud Egypt. "Awake, awake, put on strength, O arm of Jehovah; awake, as in the ancient days, the generations of old. [Art] thou not he that cut Rahab in pieces, [and] wounded the monster? [Art] thou not he who dried the sea, the waters of the great deep; that made the depths of the sea a way for the ransomed to pass over?" (vv. 9, 10). They predict their deliverance in verse 11, and Jehovah's reply to their trembling hearts in terms as full of pathos as of grandeur in verses 12-16. "And the ransomed of Jehovah shall return and come to Zion with singing; and everlasting joy [shall be] upon their heads: they shall obtain gladness and joy; sorrow and sighing shall flee away. I, I, [am] he that comforts you: who [art] thou, that thou art afraid of weak man [that] shall die, and of the son of man [that] shall be made [as] grass; and thou hast forgotten Jehovah thy Maker, who stretched forth the heavens, and laid the foundations of the earth; and thou fearest continually all the day because of the fury of the oppressor, when he makes ready to destroy? And where [is] the fury of the oppressor? The captive exile shall speedily be loosed, and he shall not die [and go down] into the pit, neither shall his bread fail. And I [am] Jehovah thy God, which stirs up the sea, that the waves thereof roar: Jehovah of hosts [is] his name. And I have put my words in thy mouth, and have covered thee with the shadow of my hand, to plant the heavens, and to lay the foundations of the earth, and to say to Zion, Thou [art] my people" (vv. 11-16).

A poetical name, signifying 'insolence,' given to Egypt. Ps. 87:4; Ps. 89:10; Isa. 51:9. The same word occurs in Isa. 30:7, where the R.V. reads "therefore have I called her Rahab that sitteth still."

(vv. 9-10) The godly recall the exercise of Jehovah's power, when at the Red Sea He broke the power of Egypt (“Rahab”), and scattered His enemies with His strong arm.

"You rule the raging of the sea; when its waves arise, You still them" (v. 9). The Lord Jesus did this literally when on earth (Mk. 4:39); and the sea of the raging nations He will completely subdue eventually, yet in the meanwhile He is ruling them behind the scenes, allowing them to go "thus far and no farther," and ordering events in such a way as to indicate His sovereign authority over them. Rahab is mentioned, that is, Egypt, the first of the nations to have held Israel in bondage, and her being broken to pieces as one who is killed. Thus, she is made an example for all of the enemies of God, whom He scatters with His mighty arm (v. 10).

Then again, on that "Arm" the godly may safely trust, for it will awake and put on strength as it did in the days of old, when it smote Egypt (Rahab) and divided the Red Sea. But now far greater purposes are in view, as enumerated in the latter part of verse 16 (Isa. 51:16). The heavens are to be planted, the foundations of the earth are to be laid; Israel in Zion is to be acknowledged as God's people.

(Vv. 9, 10). First, in view of their future blessing, the godly led by the Spirit, call for the power of the LORD to be put forth “as in the ancient days” when Jehovah delivered the nation from Egypt, and dried up the Red Sea making a way for “the ransomed to pass over.”

The first call to awake is addressed to the "Arm of the Lord." (Verse 9), for all is dependent upon Him. When the hour strikes for Him to awake and put on strength, there will be witnessed the awakening of Jerusalem, as indicated in verse 17, and again in the first verse of Isaiah 52. The awakening that will come to pass will not be merely a political or national one, but will rather involve a deep spiritual work, as is made plain when chapter 52 is reached. It will come to pass only when Jerusalem shall have suffered to the full the chastising government of God, having drunk to the dregs the cup of His fury and of their trembling.

It is the Lord Jehovah who is coming with might; but it is "His Arm" who will rule for Him. As we go through these later chapters of Isaiah we shall find the Lord Jesus presented as the Arm of Jehovah some ten or twelve times. In this character He is seen as the One who executes in power all the will and purpose of Jehovah. He is also presented as the "Servant," who is to carry out the yet more wonderful work of sin-bearing and suffering. In the passages that speak of Him as the Servant we see predictions that view Him in His first advent in grace: in those that present Him as the "Arm" our thoughts are carried on to His second advent in glory.

Isa. 51-52:12 apply the truth to the people of God or at least to the godly remnant of the future, regarded in their strict prophetic bearing. There is first a triple call: "Hearken to me, ye that follow righteousness" (vers. 1-3), "Listen (or attend) to me, my people" (vers. 4-6), and "Hearken to me, ye that know righteousness" (vers. 7-8); which indicate progress spiritually. Then follow three calls: first, "Awake, awake, put on strength, O arm of Jehovah" (vers. 9-16), a call for divine intervention; next, "Rouse thyself, rouse thyself standing, O Jerusalem" (vers. 17-23), an address to the city of God's choice; then a final "Awake, awake; put on thy strength, O Zion" (Isa. 52:1).