Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

The closing admonition is a further expansion of Deu 12:25 (see at Deu 11:21). - In Deu 12:29-31, the exhortation goes back to the beginning again, viz., to a warning against the Canaanitish idolatry (cf. Deu 12:2.). When the Lord had cut off the nations of Canaan from before the Israelites, they were to take heed that they did not get into the snare behind them, i.e., into the sin of idolatry, which had plunged the Canaanites into destruction (cf. Deu 7:16, Deu 7:25). The clause "after they be destroyed from before thee" is not mere tautology, but serves to depict the danger of the snare most vividly before their eyes. The second clause, "that thou inquire not after them" (their gods), etc., explains more fully to the Israelites the danger which threatened them. This danger was so far a pressing one, that the whole of the heathen world was animated with the conviction, that to neglect the gods of a land would be sure to bring misfortune (cf. Kg2 17:26).