"The means God appointed to help the children of Israel were to remember what was important. In his dealings with Moses, God had established a set of repetitive processes by which the Israelites would be constantly reminded of all that God had done for them. Thus, for example, in Exodus 12, God establishes the Passover Feast, the performance of which is designed in part to provoke later generations to ask the question of why this is done. This will then require parents to tell their children about God’s great act of saving grace in bringing the children of Israel out of Egypt even as this was by means of an awesome and terrifying judgment against the Egyptians.
The Passover is just one example of many rituals outlined in the Torah which functioned on one level as reminders of who God was, who the Israelites were, and how they related to each other. Thus, when we come in to the Promised Land and we find the Israelites suffering persistent recurrences of amnesia, it does not take a genius to assume that part of the immediate cause of this was their abject neglect of the means which God had established for keeping his name and his acts fresh in their minds.
What this kind of amnesia tells us is that we need constant reminders of who God is and what he has done if we are to stay on the straight and narrow; and that these are provided by the routines and rituals which God specifies in Scripture. For the Christian, under the terms of the NT age, these are the Word of God, read and preached and heard, and the sacraments, or, if you are a Baptist, the ordinances of baptism and the Lord’s Supper. These things are given to remind us of who God is; and the neglect of them will only help to accelerate any proclivities towards forgetfulness that our instinctive rebellion of God encourages."
(Carl Trueman, "Lest We Forget" in Themelios 34.3 Nov 2009: http://themelios.thegospelcoalition.org/article/lest-we-forget)