Judges 2:10

The failure of the Hebrews after their entrance into the Promised Land was rapid: one generation.

All that generation also were gathered to their fathers; and there arose another generation after them who did not know the LORD, nor yet the work which He had done for Israel.

And not really one generation, because how could that second generation not know “the work which He had done for Israel,” unless the fathers who took possession of the land did not discuss it as God commanded them? They were supposed to be talking with their children about God’s ways, God’s provision, God’s faithfulness, about God’s beautiful Torah at every opportunity. Every feast, festival, and holy day, every Sabbath, every seventh and fiftieth year, every harvest and springtime, every firstborn, every business transaction: the sum of their lives was intended to be securely bound to remembrance and worship of their God. The Lord prescribed so many interesting things in the law, hoping to inspire dialogue, to grab the hearts and attention of children and give them lifelong memories of worship that inspired and involved all their senses.

But almost from the very beginning, the people settled into the happiness and comfort the Lord provided and forgot Him, just as He said they would.

And it shall be when your son asks you in time to come, saying, "What is this?" then you shall say to him, "With a powerful hand the LORD brought us out of Egypt, from the house of slavery." ~ Exodus 13:14