What does the Torah mean when it writes "be'Ficha u'vi'Levavcha La'asoso"?
Rashi: It means that the Torah was given to us in writing (Torah she'bi'Chesav) and orally (Torah she'be'Al Peh), to fulfill it.
Ramban: It means to confess our sins and the sins of our fathers with our mouths to do Teshuvah in our hearts (to undertake never to sin again - Oznayim la'Torah), 1 and to undertake today to keep the Torah for all generations. 2
Seforno: It means to acknowledge in our hearts our sins and the G-d against whom we sinned, to be sorry and to confess on that verbally.
Targum Yonasan: It means 'Open your mouth 3 to study it, and clarify it in your hearts - in order to carry it out' 4 (Study it with the intention of fulfilling it). 5
Eruvin, 34a: It means that the Torah is only close (easy to understand) if one studies it not merely to understand it, 6 but with one's mouth and with one's heart in order to observe it.
