John Gill Commentary 2 Kings 17:39

"but Jehovah your God shall ye fear; and he will deliver you out of the hand of all your enemies." — 2 Kings 17:39 (ASV)

But the Lord your God you shall fear
Or worship him, both internally and externally, according to his revealed will; for the fear of God includes both internal and external worship:

and he shall deliver you out of the hand of all your enemies ;
that is, provided they feared and served him as he required, and it became them to do.