Isaiah 40 begins a major shift in the book. Up unto this point, the book of Isaiah has been a book of judgement, a book warning of coming punishment that will not be turned away. For many, this simply proves that God is a god of wrath. He is viewed the same way the ancient pagans saw their gods, as a deity possessed by blood rage, a god who must be appeased by the blood of some goat or he'll come after yours. At best, when reading the prophets, some see God as a legalistic judicator obsessed with balancing the scales, and without Isaiah 40 it would be easy to end our thinking there.
But Isaiah 40 changes everything. Isaiah 40 lets us see a side of God that is loving parent. A god who disciplines, yes, but not a god who delights in the pain that discipline brings. There is no blood lust in what God has done through Assyria. God is not a god who cannot control himself, who endlessly spirals into repeating patterns of wrath. God is a god who can say enough. God is a god who wants his children to live life to its fullest, and sometimes that means teaching them how far off track they have gotten. God is a god who will let his children explore and make mistakes, hold them accountable to those mistakes and make them face the consequences, but at the end of the day he will say "enough." When all is said and done, the last word is a word of comfort. It is a word that says, "Pick yourself up. Brush yourself off, and come give me a hug. I love you."
Comfort, O comfort my people. Your time out is over. Now let's go play.
Stopping point: Isaiah 41