Dora Bas Rivka Silver O'H
I Can't Begin to Imagine What G-d's Thoughts Must Be Like!
Isaiah tells all who are thirsty to go to the water and all those with no money to go buy food - it will not be an impediment. (As in many places, the food and drink are a metaphor for Torah.) Why should you work and pay for no food? Listen to G-d and eat your fill of goodness. Turn towards Him and live, enjoying an eternal covenant.
David's descendant (Moshiach - the Messiah) will chastise the nations and rule over them. You will call a nation you don't know and they will come because they've heard about the miracles G-d has performed for Israel.
Isaiah tells the people of his generation to look for G-d while He can still be found - meaning before the judgment of exile is passed. Evil people will give up their bad ways - and their bad thoughts - and return to G-d, Who will forgive them.
G-d says that His "thoughts" are not like our thoughts and His ways are not like our ways. G-d's "thoughts" (whatever that means) are as far away from ours as Heaven is from Earth. Just as rain and snow fall from the sky and they do not return without watering the Earth, the word of G-d doesn't return to Him without first "watering" those who hear it, spiritually speaking.
You will go forth from exile in joy and return to your land in peace. The mountains and trees will rejoice in song on your behalf. The wicked (compared to thorns) will be replaced by the righteous (compared to trees). This will be a permanent sign of G-d's redemption of Israel.