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.

Thou shall not hearken to the words of that prophet, or that dreamer of dreams,.... Even though he does give the sign, and work the wonder; for it might be reasonably concluded there must be fallacy in him, and that neither he nor his miraculous sign could come from God, who would never send a person to enable him to do signs and wonders, to persuade men to believe and act contrary to a former declaration of his mind and will; to break a plain law of his, as in Deuteronomy 5:7, this would be to contradict and deny himself; whatever therefore is contrary to a known law or established doctrine, either of law or Gospel, let it come from whom it will, or pretend to be confirmed by miracles, is not to be received; see Galatians 1:8,

for the Lord your God proveth you, whether you love the Lord your God with all your heart, and with all your soul; for should they be prevailed upon by such a prophet to hearken to his doctrine, and embrace it, and act according to it, it would be a plain case that they did not cordially love the Lord, since they could so easily, and by such pretences, be drawn aside from the true worship of him, and serve other gods; on the other hand, it would be a proof of their sincere affection for God, and of their close and strict attachment to him, that notwithstanding such specious pretences made, and such miracles wrought, yet abode by him and his worship, and could not be wrought upon to forsake him and follow other gods and serve them; see 1 Corinthians 11:19.

Thou shalt not hearken unto the words of that prophet, or that dreamer of dreams: for the LORD your God {c} proveth you, to know whether ye love the LORD your God with all your heart and with all your soul.

(c) God ordains all these things that his may be known.

13:3 Thou shalt not hearken to that prophet - Not receive his doctrine, though the sign come to pass. For although when such a sign or wonder foretold did not follow or come to pass, it was a sign of a false prophet, yet when it did come to pass, it was no sufficient sign of a true one, especially, in such a case. There are many things, which may be wrought by evil spirits, God so permitting it for wise and just reasons, not only for the trial of the good, but also for the punishment of ungodly men. Proveth you - That is, trieth your faith and love and obedience. To know - Namely, judicially, or in a publick manner, so as both you and others may know and see it, that so the justice of his judgments upon you may be more evident and glorious.

13:1-5 Moses had cautioned against the peril that might arise from the Canaanites. Here he cautions against the rise of idolatry among themselves. It is needful for us to be well acquainted with the truths and precepts of the Bible; for we may expect to be proved by temptations of evil under the appearance of good, of error in the guise of truth; nor can any thing rightly oppose such temptations, but the plain, express testimony of God's word to the contrary. And it would be a proof of sincere affection for God, that, notwithstanding specious pretences, they should not be wrought upon the forsake God, and follow other gods to serve them.