Early on in Parshas Nitzavim we get directions about atzvah that we are assured is not far from us (30:11),:
כִּי הַמִּצְוָה הַזֹּאת אֲשֶׁר אָנֹכִי מְצַוְּךָ הַיּוֹם לֹא נִפְלֵאת הִוא מִמְּךָ וְלֹא רְחֹקָה הִוא
A few verses later (14), it is said to even be very כִּי קָרוֹב אֵלֶיךָ הַדָּבָר מְאֹד בְּפִיךָ וּבִלְבָבְךָ לַעֲשׂתוֹ: us, in our mouths and hearts.
כִּי קָרוֹב אֵלֶיךָ הַדָּבָר מְאֹד בְּפִיךָ וּבִלְבָבְךָ לַעֲשׂתוֹ
My grandfather cites the Ramban's explanation of the mitzvah in question and offers some of his own insight. I won't cover the entire piece but focus on the part in which he addresses the Ramban's take on this as referrring to kol haTorah kula. (The other view is that it refers to the mitzvah of tshuva).
My grandfather ask, according to the Ramban's take, why refer to what is in your mouth בְּפִיךָ, for most mitzvos are not done with the mouth?
He suggests that the answer is in the mitzvah of Talmud Torah, which is fulfilled in the mouth (through enunciation of the words of Torah). The order is particularly fitting because one begins with limusd hamevi liyedey ma'ase, and also the illumination that is inherent in it directs one to good. That is to say, from the learning (which is in the mouth) בְּפִיךָ it will enter one's heart בִלְבָבְךָ, and that will bring one to to do it לַעֲשׂתוֹ. in the same order as the text.
Related post: http://kallahmagazine.blogspot.com/2015/10/dvar-yehudah-parsha-points-from-my.html