Thanks for your kind words. No, I do not have a class on Isaiah 55. I believe that the passage you mention has a fairly straightforward interpretation. "Seek the Lord while he may be found; call on him while He is near. Let the wicked abandon his way, and the sinful one his thoughts; so He may have compassion on him, and to our God, for He will freely forgive.
In this passage, God is admonishing Israel, and all of us individually, to seek a relationship with him "while He is near." How do we interpret the phrase "while he is near?" There is a sense in which God is always near. Any time we repent and turn to him, he will respond. If we are steeped in sin, God will be more distant, but like the Prodigal son, as soon as we turn, and come back to God, he is always waiting to embrace us. How long will God be near? One answer is that, as long as we are still alive, we still have a chance. However, the message of Isaiah and the Old Testament prophets is that there comes a point when it is time for judgment. We can get to the point that we are so hard-hearted, we can no longer repent. Like it says in 2 Corinthians 6:1, "Now is the day of salvation." We should not put God to the test. Like Isaiah says in v. 7, "Let the wicked abandon his way". If we do so, then as long as we are still alive, it is not too late. God will have compassion on us and will forgive our sins. Isaiah 55:6-7 is a warning, but it is primarily an encouragement for us to embrace the grace and love of God.