Have you ever heard the statement; Wake up and smell the roses.? Wake up and see what you are missing. That is what the LORD seems to be telling the sons of Jerusalem you have become passed out with drunkenness, but not with wine (51:21) - their sinfulness which led to being filled the fury of The LORD.
Verse 1 - Awake, Awake O Zion - Jerusalem continuing the theme of 51:17 - Why the call for Jerusalem not the people? Jerusalem is the heart of the nation of Judah and all of Israel -
put on thy beautiful garments - The beauty of the city under Solomon - Silver & Gold as plentiful as stones - The Glory of The LORD filled the temple - [remember the lesson on hamburger -it is when you mix the polluted outside into the safe clean inside the entire meat becomes unfit to eat unless purified by the heat]
Ps 24:4 He that hath clean hands, and a pure heart; who hath not lifted up his soul unto vanity, nor sworn deceitfully.
Zec 7:12 Yea, they made their hearts as an adamant stone, lest they should hear the law, and the words which the LORD of hosts hath sent in his spirit by the former prophets: therefore came a great wrath from the LORD of hosts
Pr 20:9 ¶ Who can say, I have made my heart clean, I am pure from my sin?
Eze 44:7 In that ye have brought into my sanctuary strangers, uncircumcised in heart, and uncircumcised in flesh, to be in my sanctuary, to pollute it, even my house, when ye offer my bread, the fat and the blood, and they have broken my covenant because of all your abominations
Malachi 1:6-8 & Isaiah 45:10
When the temple became polluted the heart of the heart of Israel became polluted and the whole nation became sick and weak. - [remember the lesson on hamburger -it is when you mix the polluted outside into the safe clean inside the entire meat becomes unfit to eat unless purified by the heat]

Eze 36:25-26 ¶ Then will I sprinkle clean water upon you, and ye shall be clean: from all your filthiness, and from all your idols, will I cleanse you. A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh.
There is a time coming when no uncircumcised or unclean person shall enter the Holy City - this is not speaking of just Jews as the Jews believe - Spiritually cleaned up by The LORD. -

The criteria to be able to enter the City will be heart that identifies you with The LORD, one He gives.
When this comes Jerusalem will be the beautiful city it once was - even more so- beauty lies not in the gold and splendor but in pure and clean hearts of those who enter and dwell there.

Verse 2- Shake off the dust and shackles of your sin their real captivity - [before you can shake off the dust what must you do? - Isaiah 51:17 - stand up. Before one who is asleep in the street with drunkenness (51:20) can stand up he must awake from his drunkenness]
Verse 3- The nation of Israel did not sell themselves into servitude for money but were placed there because of their iniquity - so they cannot be redeemed for money - (but must be redeemed of the LORD)

Verses 4&5 - While Israel owed the Pharaoh of Egypt for providing protection and sustenance he without cause showed them no mercy, The King of Assyria also showed no mercy to God's chosen as did Babylon. His chosen blasphemed His name. They were not to pay a debt owed by The LORD, He received nothing from Egypt or anyone else that He had to repay to redeem His people.

Verse 6 sets the time when this will ultimately come to pass - THAT DAY - it did not happen after Cyrus the Romans entered, it did not happen after Christ offer, the temple remained a den of thieves these offers of comfort were rejected - it that day when the remnant will escape into the kingdom and know HE IS LORD. They see Him return in is glory.
Verses 7- 10 Who is he who stand upon the mountain, has the beautiful feet, The LORD when He returns and call His people to Him. He will show Himself to them and they will see Him eye to eye. Here a redeemed nation of redeemed Jews will see, know and proclaim HE IS LORD. There will be joy and singing in Zion. When He bares His arm, that strong arm of the LORD, all the world will see His salvation, for most it will be too late - they will be on the outside looking at the pure inside.
Verse 11 - Those who handle the vessels of the LORD were the priests - the priest led the people in unclean worship. They had to clean up their hearts. Hezekiah knew this remember he made the priests sanctify themselves. This will not happen again until that day.
Verse 12 - When they are called by the LORD they do not have to worry about the enemy coming from behind because the LORD will be guarding them as they escape into the kingdom - only in That Day.

Verse 13 -15 - When the servant of the LORD rules those who were astonied or astonished before at the way he once looked, marred , looked worse than any man look before as he ruled prudently, Their question how could someone who was so marred ever stand upon the mountain in such glory. The kings of the earth will be as stone before him. Could there be things about the LORD that has never been recorded. The Lord Jesus Christ will be see and the strong arm of the LORD coming to pour out His cup of fury as He has never done before, He will proclaim judgment and justice as never before.
These verses can only be speaking o the Lord Jesus Christ, who those who looked at him on the cross could not believe how terrible he looked - as stone. When one stand before Him in judgment they will wonder how could one who allowed Himself to suffer so greatly upon that cross be this Great LORD and they will once be as stone before his throne unable to answer His judgment.
After Chapter 45 Cyrus is no longer mentioned the comfort offered through him was rejected. The comfort offered by Jesus at his first coming was rejected In "That Day" all who rejected the past comfort will stand as stone before His throne.

Wake up Jerusalem and see what you have been missing - This lesson is building to Chapter 53 that starts “Who will believe out report?”
Think about this The LORD Isaiah saw in Chapter 6 was the same LORD Moses saw in Matthew 17:1-2. Think what Isaiah felt when he saw the nail scared hands and the pierced side and the marks of the whip and thorns for the first time. Do you think he might have been in awe of the so great love The LORD had for mankind. Do you think Isaiah might have expressed - “and You went through that for me?!”