Sforno on Deuteronomy 32:46/ספורנו על דברים ל״ב:מ״ו

1אשר אנכי מעיד בכם היום, in the song of Haazinu which I use to make Israel be witness to my admonitions. The principal message is that just as while the Jewish people observe the commandments G’d arranges for their livelihood to be attained with ease and without much sweat, so, He will destroy them if they do not, because they thwart His plans for mankind as a whole.

2אשר תצוום את בניכם, near the end of your respective lives command your children to observe the matters which I have spoken to you about. It is a matter of life and death for them.

3לשמור לעשות, you have to observe all these matters in order that as their role model, your children will do so also.