Ramban

ONLY TAKE HEED TO THYSELF etc. LEST THOU FORGET THE THINGS. “[Only] then when you will not forget them and fulfill them in their true form, will you be accounted wise and understanding men; but if you pervert them due to forgetfulness you will be regarded as fools.” This is Rashi’s language. But it is completely incorrect. (take heed), it should be interpreted as a prohibition as will be explained. According to Rashi, however, it is not a prohibition, but a mere negation: if they do not observe the commandments, they will not be considered wise and understanding men. Rather, this verse, in my opinion, is a negative commandment in which he admonishes [us] severely [as follows]: For, as he stated that we should be careful concerning all the commandments and be heedful to perform the statutes and the ordinances, he again stated: “Only I warn you exceedingly to take heed and guard yourselves very, very much to remember whence the commandments came to you, that you should not forget the Revelation on Mount Sinai, nor all the things which your eyes saw there — the thunderings, and the lightnings, His glory and His greatness and His words that you have heard there out of the midst of the fire. And you should convey all the things which your eyes saw at that glorious Revelation unto thy children and thy children’s children forever.” He explained the reason [for this prohibition]: G-d made that Revelation so that you might learn to fear Him all the days and teach your children during all generations. Therefore, do so [remember the Revelation and convey it to your offspring] and do not forget it. Thus before mentioning the commandments which were proclaimed there [on Mount Sinai] he admonished with a negative commandment that we are not to forget a thing from the Revelation [of the Eternal at Mount Sinai], and we are never to remove it from our hearts. He further charged in the form of a positive commandment that we should inform all our children from generation to generation of everything that happened there — what we saw and what we heard., Vol. I, pp. 263-265). To resolve this difficulty we must say that Ramban includes the positive duty in the general commandment of teaching our children the words of the Torah (further 6:7; “The Commandments,” Vol. I, pp. 16-18), which of course includes the narrative of the Revelation. The benefit of this commandment is very great. For if the words of the Torah had come to us only through the mouth of Moses, even though his prophecy was verified with signs and wonders, yet if there [were to] arise in the midst of us a prophet or a dreamer of dreams and he were to command us [to do] the opposite of what the Torah commanded us, and he [were to] give us a sign or wonder, then a doubt would enter the people’s hearts. But since the Torah reaches us from the mouth of the Almighty to our ears, and our eyes behold that there is no intermediary, we will reject anyone who differs and who casts doubt [upon the words of the Torah] and will declare him to be false. No sign will help him, nor will any wonder save him from death at our hands for we know his falsehood. It is this which He stated there [before the Revelation], and they may also believe in thee [Moses] forever, for when we shall also transmit the matter [of the Revelation] to our children they will know that the thing was true without doubt as if all the generations had seen it, for we would not testify falsely to our children to cause them to inherit vanity and things wherein there is no profit, and they will not doubt at all the testimony we will give them. Instead they will believe for a certainty that all of us saw it with our eyes, and likewise [they will believe] all that we told them. This subject will come up again in the section, If there arise in the midst of thee a prophet, or a dreamer of dreams etc. I have already mentioned it there in the section of In the third month.