Sermons of the Sages

See my article on explanations in halacha. In short, the explanation alone is not always sufficient to establish a law. If it were not for the verse or the sermon, we would not think that the explanation is sufficient. After there is a sermon, the explanation explains it. For example, a rebellious son and not a daughter. The explanation is that the Sabbath has no way to stop them. Without the sermon, would we exclude daughters just because of the explanation? Probably not. Sometimes the explanation is decisive between two ways of demanding. When the hasbara is sufficient on its own, then the sermon is indeed only a reference. But this is only where the hasbara adds detail in the halakhah of existing Torah. When it comes to a renewed law (such as the blessing of HaNahnin), then the existence of a hasbara without a sermon is not enough to give it the status of a law of Torah. See my articles there, and also my article What is the decree of the scripture?