Myśl Żydowska do Powtórzonego Prawa 6:7

When they counted the commandments, they said: "we will not count in the negative commandments because merely refraining from them is their performance and the fulfillment of their obligation. Such service of G-d seemed too insignificant in their eyes, and their service seemed little to them due to their desire and longing for reaching the favor of G-d. Therefore they sought positive commandments of the limbs for individuals which apply at all times, places, and circumstances. They did not find any precepts that fits this except reading the torah and studying the commandments, as the verse says: "These words, which I command you this day, shall be in your heart; And you shall teach them diligently unto your children, and speak of them.." (Devarim 6:6). And the prophet (Moshe) exhorted on this a second time in saying: "You shall teach them to your sons, speaking of them, when you sit in your house and when you walk on the way and when you lie down and when you rise up" (Devarim 11:19).

Afterwards, He proceeded to the commandments of the limbs which require both thought and action, as He said: "you shall teach them to your sons".

And so that if you don't have a son, you will not mistakenly think that the (commandment of) verbally reading depends on having a son, He said: "You shall speak in them".