John Calvin Commentary Deuteronomy 18:14

"For these nations, that thou shalt dispossess, hearken unto them that practise augury, and unto diviners; but as for thee, Jehovah thy God hath not suffered thee so to do." — Deuteronomy 18:14 (ASV)

For these nations. Just as God had previously been setting before them the punishment He was about to inflict on these nations, to alarm and warn them, so now He admonishes them that the inheritance was handed over to them on this condition: that they should be mindful of such a great benefit and beware of all pollutions. They succeeded the former inhabitants of the land with the intention of being separate from them. For from where did this change come, except that God might acquire for Himself a new people and purify the land from all its defilements?

Although He only mentions two classes of superstitions, yet in this way, by synecdoche, He indicates them all. The main point is that they should not be like the nations in their vices and corruptions, which had been the cause of their destruction, since God had exterminated not only the people themselves but also their abominable rites.

Some divide the latter part of the verse into two clauses: But you shall not do so; and then, Jehovah gives you the land, for which they supply the last word. However, I do not hesitate to think that the pronoun אתה, athah, must be rendered this way: But as for you; and then I believe it must be read continuously: God has not allowed you to do so, for the word נתן, nathan, has a broad meaning.

The overall implication is that God's prohibition should carry more weight with them than the example of the nations.