When thou shalt have eaten and be full; then beware lest thou forget the Lord. - Deut 6:11-12
The people were going to a country which had long been possessed by a nation who had build cities, filled fine houses with good things, and planted vineyards. All these things the Lord would give to them. They would not have to erect houses nor plant orchards of their own.
But the danger was that when they had received all these things they would forget that they were gifts from God and would turn away into sin. We are not to forget the Giver as we enjoy the gifts.
Children that receive from their parents many good things are ofttimes ungrateful, forgetting through what toil and sacrifice these blessings have been prepared for them.
It is better for us to work ourselves for the things we get, and then we shall know their value and ever be grateful to God for them. It is always a perilous thing to forget God. To forget any friend who has been good to us is a base sin. But to forget God, to whom we owe every blessing, is the worst of all.