Notice the change of view of “that day.” The day of the Lord was seen as a horrible thing, yet God tells His people that in that day things will be restored for His chosen people. Notice the word pictures used: mountains dripping with sweet wine, hills flowing with milk, a fountain coming from the house of the LORD – all good things.
Contrast Egypt becoming a desolate wilderness to the fruitful Judah described earlier which would be inhabited forever. God’s love and mercy is great to those who trust in Him, but to those who reject Him will be utter desolation. The choice seems simple to me!