Adam Clarke on Deuteronomy 13:3

The Lord your God proveth you - God permits such impostors to arise to try the faith of his followers, and to put their religious experience to the test; for he who experimentally knows God cannot be drawn away after idols. He who has no experimental knowledge of God, may believe any thing. Experience of the truths contained in the word of God can alone preserve any man from Deism, or a false religion. They who have not this are a prey to the pretended prophet, and to the dreamer of dreams.