Isaías 51:21

"Therefore, hear now this, thou afflicted and drunken, but not with wine: Thus saith thy Lord Jehovah, and thy God that pleadeth the cause of his people, Behold, I have taken out of thy hand the cup of staggering, even the bowl of the cup of my wrath; thou shalt no more drink it again: and I will put it in the hand of them that afflict thee, that have said to thy soul, Bow down that we may go over; and thou hast laid thy back on the ground, and as the street, to them that go over."

Note the word "Therefore" in Isaiah 51:21. "Here, as in Isaiah 10:24; 27:9; and 30:18, the transition from threatening to promise is marked by the word `therefore'.[22]

The pitiful description of the Israelites' condition in the previous three verses is followed here by a dramatic change. "Now it would be the turn of Judah's brutal oppressors, who had arrogantly trampled upon the prostrate form of God's people, to drink the dreadful cup of God's vengeance."[23]

It should not be supposed that the glimpse of the arrogant and conceited oppressors of Israel in Babylon is in any manner incorrect. The most terrible behavior of that whole ancient period by those triumphant rulers and kings who gained control of unfortunate opponents was everywhere prevalent. Adam Clarke gave the example of the Emperor Valerianus, who was conquered, through treachery, and was taken prisoner by Sapor, King of Persia, who treated him as the basest and most abject slave. The Persian monarch commanded the unhappy Roman to bow him self low down and present his back as a step when Sapor mounted either his chariot or his horse![24]

Before leaving this chapter, attention should be called to the indelible earmarks which stamp this portion of Isaiah as genuine writings of the great eighth century prophet. The frequent return to subject matter found also in Isaiah 1-49, but with additional teaching, corresponds exactly with the pattern Isaiah outlined in Isaiah 28:10,13. This is classic Isaiah.

Also, notice that verse 11 here is practically a verbatim quotation of Isaiah 35:10. As Rawlinson pointed out, "Isaiah is not averse to repetitions (See Isaiah 5:25; 9:12,17,21; 10:4; 11:1; 55:25; 48:22; 57:21, etc."[25] Thus, this characteristic habit of Isaiah, appearing in both sections throughout the whole Book of Isaiah is as convincing as a signature, indicating one writer as the author of all of Isaiah.