all Israel was coming

Here "Israel" represents all the men of Israel capable of fighting. Here "all Israel" is a generalization which means almost all the men of Israel. AT: "all the men of Israel were coming" (See: rc://en/ta/man/translate/figs-synecdoche and rc://en/ta/man/translate/figs-hyperbole)

It happened that

This phrase is used here to mark where the action starts. If your language has a way for doing this, you could consider using it here.