Jamieson, Fausset and Brown on 2 Chronicles 12:7-8

7-8. when the Lord saw that they humbled themselves--Their repentance and contrition was followed by the best effects; for Shemaiah was commissioned to announce that the phial of divine judgment would not be fully poured out on them--that the entire overthrow of the kingdom of Judah would not take place at that time, nor through the agency of Shishak; and yet, although it should enjoy a respite from total subversion, [Judah] should become a tributary province of Egypt in order that the people might learn how much lighter and better is the service of God than that of idolatrous foreign despots.