What does 2 Chronicles 35:21 mean?

Neco sent messengers to Josiah, saying, 'I'm not here to fight you, king of Judah. I'm at war with someone else, and God told me to hurry. Don't get in my way, or you'll end up fighting God, who is with me, and you'll lose.' 2 Chronicles 35:21 - Modern Text Bible

(Neco tries to warn Josiah not to interfere, claiming that God has sent him on this mission and that Josiah would be opposing God if he intervened.)