"Then it shall come about when the Lord your God brings you into the land which He swore to your fathers, Abraham, Isaac and Jacob, to give you, great and splendid cities which you did not build, and houses full of all good things which you did not fill, and hewn cisterns which you did not dig, vineyards and olive trees which you did not plant, and you eat and are satisfied, then watch yourself, that you do not forget the Lord who brought you from the land of Egypt, out of the house of slavery." (Deuteronomy 6:10-12)It was inevitable that they would grow distant and drift away from God. While in the wilderness they daily saw God's presence: a cloud by day and a pillar of fire by night. They also daily experienced God's miraculous provision for their lives: fresh manna each morning and their clothes never wearing out. However, as they entered the Promised Land, things would change in two very specific ways. First, as they took possession of the land, they were dispersed far from the presence of God. Except for those who lived near where God chose to place His presence, they no longer saw or experienced His presence on a daily basis. Yes, they were to appear before God at the regular feasts, but on a day-by-day basis, they did not "know" God in any intimate way. Secondly, as the generations passed, many of the new generation had no first hand knowledge of the miracles and power of God. They had never seen the miracle of the manna, they had never seen any miraculous healings, nor had they seen the power of God expressed though His judgments. They heard stories but they lacked their own first hand account of these events. In the end, without a personal relationship with God, they drifted farther and farther, and eventually "forgot" God.
Thirdly, as the years passed, their faith with God became more cultural than experiential.
"When your son asks you in time to come, saying, 'What do the testimonies and the statutes and the judgments mean which the Lord our God commanded you?' then you shall say to your son, 'We were slaves to Pharaoh in Egypt, and the Lord brought us from Egypt with a mighty hand. Moreover, the Lord showed great and distressing signs and wonders before our eyes against Egypt, Pharaoh and all his household; He brought us out from there in order to bring us in, to give us the land which He had sworn to our fathers. So the Lord commanded us to observe all these statutes, to fear the Lord our God for our good always and for our survival, as it is today.'" (Deuteronomy 6:20-24)While the Israelites were very good at passing down their national history, they failed to instill their faith in God from generation to generation. They had a cultural awareness of God and His work in the forming of their nation, but they lacked the present day faith and vital relationship with God that He seeks with all His people. Knowledge and history of God is not enough, we need faith and a relationship with God. Without such a relationship, any covenant with God is doomed to failure, even from the start.