The book of Isaiah forms a double entendre of meaning, first giving to its hearers in its immediate context the coming judgment for sin; and at the same time presenting a grander spiritual revelation of a coming Messiah who would bring deliverance to those who would respond to Him as Lord.
To be sure, the Judeans of Isaiah's day were engrossed in their flagrant sins against the Lord; in fact, they had gotten to a point that their rebellious behavior was not something that they would hide in secret. Instead, they would flaunt their sinful ways in public, openly defying the One True God to whom they were called to submit and obey. God had been quite merciful to the Judeans in sending prophets like Isaiah to warn them to repent of their wickedness, but these people had reached a point of such debasement that God would chose to enact His righteous wrath. Whereas God had given to these Israelites the blessing of the "flowing waters of Shiloah" (i.e. the Promised Land), this covenant people decided that they would long after the pagan ways of the Arameans and the northern tribes ("Rezin and the son of Remaliah"). No longer did they want God's best for them; rather, they desired to satisfy the cravings of their selfish, evil hearts. They chose to worship themselves over God, and they decided to shake their rebellious fists in the face of God just daring that He do something about their sacrilege towards Him.
God gave the prophet Isaiah His word of judgment against the Israelites, and of His judgment upon the people . . . a river would sweep over the people with unexpected fury to the point that they would be up to their necks in the waters of wrath with no apparent rescue. Then God ends the excerpt with the words, "O Immanuel!" or (O God with us!). In the seemingly hopeless circumstance in which the people would find themselves, the "zeal of the Lord" would provide a Deliverer to them. This grace would be manifest in the birth of the God-child who would be the "great light" to those walking in darkness. Of course, the prophecy described in Isaiah 9 of a Savior would ultimately be fulfilled in the Christ child born to the world some 700 years later in Bethlehem, to provide salvation to those who would respond to Him in faith.
Still, some will refuse to receive God's offering of deliverance from His wrath. With pride and arrogance of heart, the people will say, "we've had some misfortune . . . but we can provide our own deliverance. We are in no need of a Savior, for we are our own gods/saviors to whom we will continue to offer our worship." They will continue to seek their own sinful ways over the Lord; and in response, God will serve upon them His eternal judgment, from which there is no escape. God will ultimately thrust these people into the "utter darkness" of hell, from where no remedy can be found (8:22); when this point is reached, His anger will not be turned away, but will fall upon these recalcitrant ones for all eternity.
If there has ever been a presentation of the gospel in Scripture, it is found here, for we all are "ungodly and wicked" (9:17), and are thus in need of God's offering of Himself as our Savior. God has paid the ultimate sacrifice for our sins through His death on a cross, and His power over sin and death were demonstrated through His resurrection. Now, His offer of grace is presented to each of us, provided that we respond to His offering with faith, repentance, and surrender. For those who would submit to Jesus Christ as Lord, God imparts the blessedness of His mercy. To those who would continue to assert their own quest for lordship and therefore defy God's offering of salvation, only eternal judgment awaits.
May we all regularly reflect upon the offering of God's grace to us, and may this reflection stir within our hearts the desire to honor the One True God.