Deuteronomy 31:21

It shall not be forgotten: this seems not to be a precept that they should remember it, but a prediction, that God would give them sad occasion to remember it, by bringing upon them the dreadful calamities mentioned in it. Their imagination which they go about, even now; either their inward inclinations to idolatry, which they do not check, as they ought, but rather entertain with delight; and some of them do not only cherish it in their hearts, but as far as they can and dare secretly practise it, as may be gathered from Amos 5:26 Acts 7:43; or their secret purposes to allow themselves therein, when they are settled in their land, which were clearly known to God, though it may be not fully evident to themselves.