John Calvin Commentary Deuteronomy 18:9

"When thou art come into the land which Jehovah thy God giveth thee, thou shalt not learn to do after the abominations of those nations." — Deuteronomy 18:9 (ASV)

When you are come. It is too well known from experience how eagerly the human race lays hold of bad examples, and how prone it is to imitate them. Especially those who come into a foreign land readily accustom themselves to its manners and customs. This is the reason why God expressly commands the Israelites to beware, lest when they come into the land of Canaan, they should catch any infection from its inhabitants. The doctrine, indeed, is universal in its application, but there was a necessity for providing against the danger that was immediately imminent. Moreover, Moses clearly explains in this passage what it is to have other gods, namely, to mix the worship of God with profane things, since its purity is maintained only by banishing from it all incompatible superstitions. The sum, therefore, is that the people of God should abstain from all human inventions by which pure and simple religion is adulterated.

In general, God wished to deter His worshipers from every fallacy by which, from the beginning, Satan has deluded and fascinated miserable people. He enumerates certain particular points that by usage and custom had become most prevalent. But so that God’s purpose may be more apparent, it is beneficial to observe what it is that displeases Him in these vices which He condemns.

Since humans have a natural desire for knowledge, even in the superstitious this desire has always proceeded from a good principle, because God has implanted it in the minds of all, as He intended to distinguish our race from the lower animals. Nor was there anything blameworthy in this: that people, being conscious of their own ignorance, believed they were to obtain knowledge only by consulting God. Now this was the sole object of the Gentiles when they inquired of their magicians and sorcerers: to seek from heaven that knowledge which they perceived themselves to lack. Thus they undoubtedly confessed themselves to be overwhelmed with darkness and acknowledged that the light of understanding was the special gift of God. From this also came the name of divination, because they were persuaded that secret things were not within human understanding, but that this knowledge must come from divine inspiration.

But since by his schemes the devil perverts what is inherently right, these principles implanted in us by nature, as I have said, have been corrupted by two errors: an immoderate desire of knowing more than is lawful has crept into our minds, and then we have resorted to illicit means of knowledge. From these sources, namely, foolish curiosity and unrestrained recklessness or audacity, all the superstitions and errors have flowed by which the world has been assailed.

Therefore, God, by forbidding magical arts, introduces a remedy for these two diseases. These arts were perversely invented so that they might search out and bring to light things that He had chosen to conceal. For the best rule of knowledge is sobriety, so that it may be enough for us to know as much as is beneficial for us. The lust of people has carried them deeper, so that they have desired to penetrate into all the most profound secrets. But the second error on which I have touched is much worse: that they sought by improper means to discover hidden things.

We will soon see that God also has foretold future events by His servants, but no further than He knew to be profitable, and only with this object: to make it manifest that He exercises special care for His church. But since human curiosity is insatiable, people do not consider what is useful for them but, like Adam, desire to “be as gods,” and to know all things without exception. When God does not indulge these improper desires, they turn to the devil, the father of lies, still, however, as I have stated, under the false disguise of God’s name. This is the origin of all the vanities by which the world has ever been entangled. I will now turn to specific points.