Winepress of Wrath
God is pictured as returning from battle with Edom, Bozrah being the chief city of Edom. This ties in with many prophecies of Edom's destruction at Christ's return. Indeed, Obadiah states that there will be no Edomites left alive during Christ's reign (Obadiah 18). Yet, in context here, Edom seems to be used as a general representation of Israel's enemies since God mentions treading down the "peoples" (verses 3, 6). As was explained in the comments on Obadiah and Isaiah 34, there may be a connection between Edom and the future Babylon, the preeminent national foe of the end time—that is, a significant portion of Edomites may end up being part of this system.
Christ's garments are stained with blood because of the vengeance He has taken on the enemies of His people, something He has had to take care of by Himself since no one was found to help Him (verses 1-6). The winepress imagery—squeezing out the "blood" of grapes—as a figure of judgment can also be found in Joel 3:13 Joel 3:13Put you in the sickle, for the harvest is ripe: come, get you down; for the press is full, the fats overflow; for their wickedness is great.
American King James Version×, Lamentations 1:15 Lamentations 1:15The LORD has trodden under foot all my mighty men in the middle of me: he has called an assembly against me to crush my young men: the LORD has trodden the virgin, the daughter of Judah, as in a wine press.
American King James Version×, Revelation 14:17-20 Revelation 14:17-20  And another angel came out of the temple which is in heaven, he also having a sharp sickle.  And another angel came out from the altar, which had power over fire; and cried with a loud cry to him that had the sharp sickle, saying, Thrust in your sharp sickle, and gather the clusters of the vine of the earth; for her grapes are fully ripe.  And the angel thrust in his sickle into the earth, and gathered the vine of the earth, and cast it into the great wine press of the wrath of God.  And the wine press was trodden without the city, and blood came out of the wine press, even to the horse bridles, by the space of a thousand and six hundred furlongs.
American King James Version×and 19:15.
A God of Great Mercy
Then, in a moving description, Isaiah tells of the loving-kindness (Hebrew hesed, “covenant faithfulness" or "steadfast love") God has for His people, in spite of their depraved behavior (Isaiah 63:7 Isaiah 63:7I will mention the loving kindnesses of the LORD, and the praises of the LORD, according to all that the LORD has bestowed on us, and the great goodness toward the house of Israel, which he has bestowed on them according to his mercies, and according to the multitude of his loving kindnesses.
American King James Version×). God is quoted as saying: "Surely they are My people, children who will not lie" (verse 8; see Exodus 24:7 Exodus 24:7And he took the book of the covenant, and read in the audience of the people: and they said, All that the LORD has said will we do, and be obedient.
American King James Version×). He is pictured as trusting their honesty in remaining faithful to Him as they had promised, and He helped them in all their trials. Their rebellion grieved Him tremendously, yet God still remembers the old days fondly. And Isaiah reminds God of this in His appeal for mercy and help.
God putting "His Holy Spirit within them" in Isaiah 63:11 Isaiah 63:11Then he remembered the days of old, Moses, and his people, saying, Where is he that brought them up out of the sea with the shepherd of his flock? where is he that put his holy Spirit within him?
American King James Version×can also be translated as God putting "his Holy Spirit within him" (KJV and J.P. Green's Literal Translation)—that is, within Moses, who is mentioned earlier in the same verse. Indeed, this must be the case since God's Spirit was not given to the Israelites as a whole.
Israel's prayer for mercy and deliverance is continued in chapter 64. Verse 4 is quoted by Paul in describing the ignorance of those who crucified Jesus, not understanding the wisdom of God, and explaining that we, however, can understand through His Spirit (1 Corinthians 2:6-11 1 Corinthians 2:6-11  However, we speak wisdom among them that are perfect: yet not the wisdom of this world, nor of the princes of this world, that come to nothing:
 But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world to our glory:
 Which none of the princes of this world knew: for had they known it, they would not have crucified the Lord of glory.
 But as it is written, Eye has not seen, nor ear heard, neither have entered into the heart of man, the things which God has prepared for them that love him.
 But God has revealed them to us by his Spirit: for the Spirit searches all things, yes, the deep things of God.
 For what man knows the things of a man, save the spirit of man which is in him? even so the things of God knows no man, but the Spirit of God.
American King James Version×).
In Isaiah 64:6 Isaiah 64:6But we are all as an unclean thing, and all our righteousnesses are as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away.
American King James Version×, the people confess that their own righteousness—that is, their attempts to obey Him without His spiritual help and their living by what they themselves consider righteousness as opposed to true righteousness—are as worthless and repulsive as "filthy rags." Says the JFB Commentary, “lit[erally] a 'menstruous rag'" (note on verse 6). Or The Nelson Study Bible: "Garments stained during menstruation…making a woman unclean (Leviticus 15:19-24 Leviticus 15:19-24  And if a woman have an issue, and her issue in her flesh be blood, she shall be put apart seven days: and whoever touches her shall be unclean until the even.  And every thing that she lies on in her separation shall be unclean: every thing also that she sits on shall be unclean.  And whoever touches her bed shall wash his clothes, and bathe himself in water, and be unclean until the even.  And whoever touches any thing that she sat on shall wash his clothes, and bathe himself in water, and be unclean until the even.  And if it be on her bed, or on any thing where on she sits, when he touches it, he shall be unclean until the even.  And if any man lie with her at all, and her flowers be on him, he shall be unclean seven days; and all the bed where on he lies shall be unclean.
American King James Version×; Ezekiel 36:17 Ezekiel 36:17Son of man, when the house of Israel dwelled in their own land, they defiled it by their own way and by their doings: their way was before me as the uncleanness of a removed woman.
American King James Version×)" (note on verse 6). Paul describes Israel's dilemma in this regard in Romans 10:1-3 Romans 10:1-3  Brothers, my heart's desire and prayer to God for Israel is, that they might be saved.  For I bear them record that they have a zeal of God, but not according to knowledge.  For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves to the righteousness of God.
American King James Version×—and explains in the following verses that the answer they need is Christ for righteousness. That is, they need the justification that comes through His sacrifice and the ongoing obedience that comes from His living in people—as He transforms them as a potter does clay (Isaiah 64:8 Isaiah 64:8But now, O LORD, you are our father; we are the clay, and you our potter; and we all are the work of your hand.
American King James Version×).
Isaiah is able to see, through the visions God has given him, the eventual destruction of Jerusalem, including the temple: "Our holy and beautiful temple, where our fathers praised You, is burned up with fire" (Isaiah 64:11 Isaiah 64:11Our holy and our beautiful house, where our fathers praised you, is burned up with fire: and all our pleasant things are laid waste.
American King James Version×). It was something very distressing to him, and added to his emotional turmoil.