God invites the people to join in this new covenant, saying that the thirsty should come and drink and the people without money should come and eat. He then points out that people are wasting their time and money on things that "do not satisfy." Ah, we gotcha. God's talking about spiritual sustenance. Clever.
Because he loved King David back in the day, as a sort of homage, God's gonna bless all of his people in a new covenant.
God predicts that all the nations will come running, drawn to Israel's splendor like moths to a flame (or Shmoop to an In 'n' Out).
Isaiah urges the people to return to God. If the wicked give up their evil ways, they'll definitely find their pardon because God is really merciful.
God reminds the reader that his thoughts and ways are different from those of humans—specifically, they're "higher," and presumably, more awesome.
His word is going to be like rain or snow which pours down on the land to make the vegetation grow. And the word won't return to God until it has successfully accomplished this purpose.
The people will go out in joy and peace, and everything in nature—mountains, hills, fields, and the whole shebang—will join them in celebrating.