Charles Spurgeon Commentary 2 Kings 17:25-27

"And so it was, at the beginning of their dwelling there, that they feared not Jehovah: therefore Jehovah sent lions among them, which killed some of them. Wherefore they spake to the king of Assyria, saying, The nations which thou hast carried away, and placed in the cities of Samaria, know not the law of the god of the land: therefore he hath sent lions among them, and, behold, they slay them, because they know not the law of the god of the land. Then the king of Assyria commanded, saying, Carry thither one of the priests whom ye brought from thence; and let them go and dwell there, and let him teach them the law of the god of the land." — 2 Kings 17:25-27 (ASV)

He did not care one single bit himself what their religion was. But if they did not happen to have a religion to suit the country, "Well, then, send one of the priests who used to live there who can teach them what it is." According to his notions, they could take it up just when they liked.