“They feared the Lord, and served their own gods” [II Kings 17:33]

“They feared the Lord, and served their own gods” .A priest was sent into their midst to teach them how they should fear the Lord: but this was done alongside the existing idolatry in the land.
Earlier we read how, when professing to follow the Lord, the children of Israel secretly did those things against the Lord that were not right. Their apparent godliness was a pretence or show, like a shop window dressed to create the impression that all was well inside. But inside their homes, those who came to dwell in Samaria, worshipped all kinds of gods.
If they wanted to avoid a repetition of the judgment brought when lions rampaged among the people, this was the wrong way to go about it. Worshipping the Lord must be an exclusive engagement.