So the king of the south - Ptolemy Euergetes: -
Shall come into his kingdom - That of Seleucus Callinicus.
And shall return - Having heard that a sedition had taken place in Egypt, Ptolemy Euergetes was obliged to return speedily in order to repress it; else he had wholly destroyed the kingdom of Callinicus.
So the king of the south shall come into his kingdom - That is, into the kingdom of the north, or the kingdom of Syria. This verse seems to be a summary of what had been said about his invading Syria. He would come, on account of the wrongs done to his sister, into the kingdom of the north, and would then return again to his own land.