Hearing the voice as well as the words
Keep and listen to all these words שְׁמֹר וְשָׁמַעְתָּ אֵת כָּל הַדְּבָרִים הָאֵלֶּה
My grandfather references the Ohr Hachaim's interpretations which includes this take on the juxtaposition of keeping and listening: if you wish to understand the truth of Torah, you have to keep the mitzvos. In other words, the acceptance of mitzvos is a prerequisite for intensive Torah study.
In a similar vein, my grandfather says, he has explained Chazal's take of na'ase venishma, [we will do and we will listen] which prompted the exclamation, Mi gila livni raz zeh [who revealed this secret to my children?] That is because the na'ase is the condition for the nishma. Without a commitment to the mitzvoss, it is impossible to plumb the depths of the Torah's secrets. How lofty is the spiritual level of Yisrael that they were able to reveal this secret!
Further on in this Parsha 13:5, it says וְאֶת מִצְוֹתָיו תִּשְׁמֹרוּ וּבְקֹלוֹ תִשְׁמָעוּ [keep His mitzvos and listen to His voice]. Again, the shmira preceeds the shmia. Rashi and Ramban there interpret וּבְקֹלוֹ תִשְׁמָעוּ as referring to the voice of the neviim [prophets].
My grandfather suggests another extension on the interpretation of listening there as an obligation to keep not just the mitzvos that are stated explicitly but also to walk bederech hachaim, that is to live according to da'as Torah, what it is possible to discern to hear from the kol [voice] even if the words are not expressed. [This concept is often expressed in terms of being true to the spirit as well as the letter of the law.]The same can be applied to the first verse we quoted here.
Related post: http://kallahmagazine.blogspot.com/2015/10/dvar-yehudah-parsha-points-from-my.html