What exactly is the Mitzvah of "Velimadtem osam es Beneichem ... "?
Seforno: It is an obligation to accustom one's children to keep the Mitzvos.
Why does the Pasuk add the words "Ledaber bam"?
Rashi: To teach us that, the moment a child is able to speak, one should teach him to say the Pasuk "Torah Tzivah lanu Moshe ... ". And from here, Chazal learned that as soon as the child is able to speak, his father should speak with him in Lashon ha'Kodesh and teach him Torah. 1
Rashi: Otherwise, it is as if he has buried him.
Having already stated "Vedibarta Bam" in (6:7), why does the Torah repeat it here?