The people of Yehudah relied on the Temple service, per se, to atone for all their sins. The name of the altar, "Ariel," became a cliche, as if just repeating the word atoned for all sins. The altar did have power to atone for sins, but not when relied upon with abuse. So, whereas once old sins were erased from the records, now they were added to the previous years.
Jerusalem's troubles will all come from G-d - it is He Who will encircle and besiege it. Sancheiriv or Nevuchadnetzar are only His agents. It is He Who will storm it with arrows and boulders catapulted from the surrounding ramparts, both during First and Second Temple times.
"Contemplate and consider, reflect and talk about this; you are drunk, but not from wine; dizzy, but not from liquor. For G-d has poured upon you a spirit of deep trance, closing your eyes and those of the prophets, and covering those of your leaders, the seers." - Isaiah 29:9-10
But the salvation of Yehudah under Chizkiyahu will be only temporary; afterwards, they will corrupt their ways. Although they later turned to wine, that was the symptom, not the cause. The underlying cause was that they had forsaken the Word of G-d - they devoted no time to its study. If only they would reflect on their ways, perhaps, they would see this real cause of their confusion, their "drunkenness." Because they learned not G-d's Word, they fell into spiritual sleep. This influenced the entire generation, even those who strived for prophecy.
"G-d then said, "Because this people has approached to honor Me with their mouths and lips while distancing their hearts from Me, their awe of Me only as people fulfilling obligations taught to them, I am therefore going to cause this people to be an astonishment, an astonishing astonishment: the wisdom of their wise shall be lost and the understanding of their understanding ones shall be hidden."" - Isaiah 29:13-14
Because the people ceased learning the Teachings of G-d and thus "distanced their hearts" from Him, because they served Him only out of a feeling of "obligation" and not out of an inner desire; because they approached G-d only when they had a need and prided themselves in doing so; because they approached Him only with empty lip service and not with a service of soul, therefore G-d will so punish them that all who see them will be astonished. The people once known for their great wisdom had become lax in their search for more. Measure for measure, they shall lose what they have and have no teachers to guide them anymore. Their wisdom shall be lost - lost to plagiarizing nations, who will "hide" Jewish wisdom within their own.
"Woe to those who try to hide from G-d and to conceal their plans from Him! Their deeds are done in darkness, saying, "Who sees us, who knows about us?" How contrary! Are you like the raw material of a craftsman which, as finished product, says to its producer, "You have not made me?" But can the creation say to its Creator, "You do not understand me?" - Isaiah 29:15-16
And because they ceased learning the Word of G-d, they lost faith in G-d's sustaining Presence. They thought that G-d may have created the world, but since then, it has no need for His Presence. They thought that the world is like the vessel which is independent of the one who made it. Thus they thought that they could do as they please, for G-d, anyway, takes no notice. But how wrong are they, those who think that way! - they know not the truth of Creation. They compare creation to a product which can almost say to its maker, "You have not made me!"
"For in a very short time the Lebanon shall become like the farmland and farmland shall become like a forest." - Isaiah 29:17
But, nevertheless, all is not lost and a return to G-d will change everything. G-d will restore the wild forest to a settlement and a settlement will become a "forest" of cities.
"The deaf shall then hear the written word and the blind shall see in the darkness. The humble will then intensify their rejoicing in G-d and the most needy of people will rejoice in the Holy One of Israel." - Isaiah 29:17
G-d will then reopen their ears and eyes to understand His Teachings and to see His Presence - to see it in the "darkness," in their troubles. Even those whose comprehension was "humble" and were "needy" of mind shall then attain great understanding and will rejoice in their knowledge of G-d.
"For the violent will cease and scoffers shall perish, all seekers of evil will be destroyed: those who make others sinful with words, those who set traps for he who remonstrates at the gate and those who falsely wrong the righteous." - Isaiah 29:20-21
Then, all evil will cease; those who do evil maliciously, the "violent," and those who mock the words of the wise, the "scoffers"; those who seduce others into sin, the "seekers of evil," and the false prophets who "make others sinful with their words;" and also those who malign the true prophets, who "falsely wrong the righteous."
The time will yet come when G-d will redeem the Jewish people, just as he redeemed Abraham from the Chaldeans. The Jewish people will then not behave in a way to cause themselves shame. All of them will then be called after Jacob whose children were all righteous (as opposed to Abraham who had Ishmael and Isaac who had Esav) and will now be sanctifying G-d's Name. Then the people will learn G-d's Teachings - even the confused and agitators.