Isaiah 6:11, “How long, Lord?”
In each of the four gospels, in Acts, and in Romans, Isaiah 6:9-10 is quoted. The most complete example is in Acts, and occurs right at the end of the book. [Acts 28:25-31]
The account of Paul’s ministry ends rather abruptly, and many think that the original conclusion of the book of Acts is missing. Other references to Isaiah 6:9-10 are Matthew 13:14-15, Mark 4:12, Luke 8:10, John 12:40, and Romans 11:8.
In the following I focus on the next verse, in which the prophet Isaiah asked for how long the real meaning of prophecy will be hidden, and the answer he was given. On Isaiah 6:11 and 12, Princeton professor Joseph Addison Alexander commented: 
11. And I said, How long, Lord? And he said, Until that cities are desolate for want of an inhabitant, and houses for want of men, and the land shall be desolated, a waste, or utterly desolate. The spiritual death of the people should be followed by external desolation. The common explanation is no doubt the true one, that the Prophet asks how long the blindness of the people shall continue, and is told until it ruins them and drives them from their country. As the foregoing description is repeatedly applied in the New Testament to the Jews who were contemporary with our Saviour, the threatening must be equally extensive, and equivalent to saying that the land should be completely wasted, not at one time but repeatedly.
12. This verse continues the answer to the Prophet’s question in the verse preceding. And (until) Jehovah shall have put far off (removed to a distance) the men (or people of the country) and great (much or abundant) shall be that which is left (of unoccupied forsaken ground) in the midst of the land. This is little more than a repetition, in other words, of the declaration in the verse preceding. The terms of this verse may be applied to all the successive desolations of the country, not excepting that most extreme and remarkable of all which exists at the present moment.
Since Alexander’s time, a Jewish state has been established in Palestine. Many Jews have migrated there. But there has been no fulfillment of Isaiah 6:11-12. If the land was previously desolate, and without inhabitant, and is now inhabited by God’s people, wouldn’t Isaiah’s prophecy imply that the time when the meaning of his prophecies would be known had come?
Evidently, Isaiah must have referred to another land. The prophecy could refer to the land of promise in its spiritual sense. It can’t be the literal land, in the sense Alexander supposed above. The Jewish people now living in the modern Jewish state are no more enlightened about the Gospel, than the Jews of Rome were when Paul was there, and when the last verses of the book of Acts were written.
Alexander interpreted the land in a spiritual sense, in his comments on Isaiah 57:13, where he explained “he that putteth his trust in me shall possess the land” as having “a wider explanation, in which the possession of the land is an appointed symbol of the highest blessings which are in reserve for true believers here and hereafter.”  This is the spiritual meaning of the land; the land of Canaan was a type and shadow of the spiritual blessing promised to believers.
Ebenezer Henderson (1784-1858) understood the healing mentioned in Isaiah 6:10 as referring to spiritual conversion, and the forgiveness of sins. He wrote, “The healing referred to is the entire moral recovery which sinners experience on their conversion to God; and, as pardon is essential to such recovery, healing and forgiveness of sins came to be regarded by the Hebrews as synonymous.”  Henderson commented on the Hebrew terms used in verse 11: 
11. עַ֣ד אֲשֶׁר֩ אִם This accumulation is designed to give intensity to the statement, and thereby to intimate, in such connexion, the great length of time during which the obstinacy of the Jews should be evinced. Comp. Gen. xxviii. 15; Numb, xxxii. 17. תִּשָּׁאֶ֥ה שְׁמָמָֽה lit. be laid waste, a desolation, for “be utterly wasted.”
Like many scholars, Otto Kaiser thought that the prophecy of Isaiah 6:9-11 re