Deuteronomy 4:9

Only take heed to thyself. — The exhortation contained in the following verses lays special emphasis on one point — the worship of the invisible Jehovah without images. This more than anything else would tend to separate the religion of Israel from that of all other nations.

Teach them thy sons, and thy sons’ sons. — A command which Israel evidently failed to obey. For a generation speedily rose up “which knew not Jehovah nor yet the works which he had done for Israel” (Judges 2:10). It is worth while to observe that we cannot find any trace of a system of national education in Israel until many years later. When education is purely parental, it is likely to be neglected in many instances. It is not every parent who finds himself able to “teach his sons, and his sons’ sons.”