The Jewish people are considered the "Children of G-d" and as such, should follow His Will. When a child is in danger or needs some form of help, to whom shall he turn, if not to his father? Woe to the child who does not do that, for he will not get the protection of his father.
"For they are a rebellious people, faithless children, children who refuse to listen to G-d's Teachings. They say to the seers, "Do not see," and to the prophets, "Do not prophesy truths. Tell us, rather, flattery and prophesy mockery. Turn aside from the Path and leave the Way, cease to confront us with the Holy One of Israel." - Isaiah 30:9-11
And the reason is because they were a rebellious people who deny the sins that they do. They are "faithless" because they even deny being G-d's children. They brazenly tell the prophets of G-d not to speak in His Name and not to rebuke them, but rather to just placate them that all will be well - they do not want to confront G-d.
"For thus says G-d, the Lord of Hosts, the Holy One of Israel: "You can be saved with peace and tranquility, your might can come through calm and trust" - but you were not interested. - Isaiah 30:15
G-d had warned them through His prophets that He would save them if they turned to Him. They would be able to sit down calmly within their homes because G-d would save them for their trust in Him.
"Therefore G-d shall tarry in showing you grace and will hold back from granting you mercy. For the Lord is a just G-d - happy are those who wait for Him!" - Isaiah 30:18
The purpose of this prophecy of destruction is so that the Jewish people repent and seek G-d, rather than seek foreign powers. G-d's intent is not to destroy, so He will tarry in carrying out this judgment. He will wait to see if you will repent, in which case, He will show you mercy. Just as He punishes those who rebel, He will forgive those who return to Him. Happy are those who wait for His mercy and woe to those who despair of it!
"For the people in Tzion shall dwell in Jerusalem - cry not, for G-d will surely show you grace at the sound of your cry and answer you as soon as He hears." - Isaiah 30:19
Although the Jewish people will go through a time in which they will remain in the Land "like a lonely mast atop a mountain," the time will yet come when they will live safely in Jerusalem and G-d will answer them as soon as they call to Him.
"Your ears will then hear something coming from behind you saying, "This is the path, walk along it, whether to the right or to the left." - Isaiah 30:21
So great will then be their desire to hear the Word of G-d, that they will even "hear" things not addressed to them - they will understand they message which G-d is sending them in everything that they see. And even when one will be tested with sin, he will clearly hear that "voice" behind him saying, "No, not that! This is the way!" This voice will be their guiding light, whether it brings them material benefit - "to the right" - or not - "to the left."
"The light of the moon shall then be like the light of the sun and the light of the sun shall be sevenfold like the light of the seven days, when G-d will bandage the wounds of His people and heal the blow of their injuries." - Isaiah 30:26
The darkness of exile will be replaced by the Light of Redemption, a Light which also symbolizes material blessing. But even in simple, physical terms, the moon's light will then nurture growth on earth as the light of the sun does now.
"Lo, the name of G-d is approaching from far, with burning rage and as a heavy burden: His lips are full of fury and His tongue is like a consuming fire." - Isaiah 30:27
The nations who will march against Jerusalem, like Sancheiriv had done before them, will think G-d is far away and will not come to the help of His people. This is not so, for already, in "far away times," G-d has shown how He comes to the aid of His people, as when he redeemed them from Egypt. And when He does so this time, it will be a "heavy burden to hear." But this verse is not only referring to the Future, but also to the times of King Chizkiyahu after Sancheiriv's fall.
The nations shall be swept away as if by a torrent stream, shaken up as if with a largeholed sieve which holds nothing back - shaking them up just to shake them. They will be misled into thinking that they can take Jerusalem, which will only bring them to their downfall.