The second phrase of this passage is what caught my attention. This translation and some others use the phrase "an acceptable time", while others use the phrase "a favorable time". I think the translations best catch the spirit of the passage that include both the words "favorable" and "acceptable" to describe when God works.

God always acts in a favorable time, in the time that allows us to receive the best of God's blessings for us. God always acts in an acceptable time, in the time that best fits God's good and perfect will for us. The core of our faith should be that God knows what is best for us, God always chooses to do what is best for us, and God's timing is always perfect. We are to live by the faith that God is working out in God's time what will develop us into what we are meant to be.

Isaiah describes what God is going to do in glorious terms, especially in contrast to his stern messages of the more immediate punishment that will come from the people's rejection of God. God through Isaiah wants to remind all of us that the cost of our rebellion is separation and punishment, but that even in difficult times, God is working to make us stronger believers, better servants, and truly blessed followers.

The timing of the people's response in this passage shows the kind of faith God wants us to have. It starts with the timing of God's actions presented in this passage--even though God had not yet allowed Judah to fall, God was already speaking of grace and reconciliation after the people repented as if these events had already taken place. Isaiah called on the people to be so certain of God's goodness that they would express thanks in advance of what God was going to do. Of course we sing and rejoice in response to how God has blessed us in our past. Faith calls on us to have such confidence in God's timetable that we sing and rejoice now for what is yet to come, knowing that God's goodness and faithfulness to us is a certainty.