Komentarz do Powtórzonego Prawa 30:14

כי קרוב אליך BUT [THE WORD] IS [VERY] NEAR UNTO YOU — the Torah has been given to you in writing and orally.

בפיך ובלבבך לעשותו, to recognise with your heart the nature of your sins and the One against Whom you have sinned so that you will express your confession and remorse to Him with your heart and with your lips.

בפיך ובלבבך לעשותו, “with your mouth and your heart to perform it.” The Torah mentions three things here; the mouth, the heart, and the performance. All the laws of the Torah are included therefore as belonging to one of these three categories. There are commandments which require to be fulfilled by use of the mouth; others can be fulfilled by means of the heart only; still others require “performance,” i.e. the involvement of other organs and parts of our bodies. This is what may have prompted our sages in Avot 1,20 to state that “the world stands on three things, on Torah, on service to the Lord, and on the performance of deeds of loving kindness.” When the sages said: “on the Torah,” they meant on our engaging our mouth in the service of the Lord; when they said: “on service to the Lord,” they meant that our hearts had to be involved in fulfilling the commandments. Commandments which require the participation of our heart rank higher than those which can be discharged by means of only our mouths. This is the reason that when someone who is engaged in studying Torah (using his mouth to serve the Lord) must interrupt his studies when it is time to perform a commandment requiring our heart, i.e. the reading of the first line of the Kriyat Shema. (compare Shabbat 11) According to Rabbi Yehudah haNassi (Berachot 13) it is only the first verse in that paragraph which requires the kind of concentration that one must interrupt regular Torah study in order to perform it properly.
Mitzvah-performance which necessitates the mouth is ranked higher than the performance of commandments which involve other parts of our body such as offering sacrifices. (Tanchuma Tzav 14) This is based on Leviticus 7,31 seeing it does not say זאת התורה , עולה וגו' but זאת התורה לעולה, למנחה, וגו', “i.e. that there are viable or even superior alternatives to the offering of sacrificial animals. Ed.] This is the reason the word ובלבבך has been written in the middle of the three categories, to emphasize its centrality, the fact that it is the most important of the three. This is why performance, i.e. with the limbs and organs of the body, has been written only at the end of the verse.
Nachmanides, at the end of verse 11 writes as follows: the words בפיך ובלבבך refer to the subject of penitence, repentance, a commandment spelled out in verse 2 of our chapter. When the Torah speaks of this repentance it draws attention to the fact that it is not so difficult to fulfill this commandment. The Torah does not demand all sorts of difficult tasks such as ascending to heaven or crossing the ocean for a person to have fulfilled this commandment. All it takes to become a true penitent is the mouth and the heart. It may be performed anywhere; you do not even have to come to Jerusalem and the Temple to have your repentance accepted by the Lord. It is the easiest thing to do, i.e. כי קרוב אליך הדבר מאד לעשותו, “the matter is right at hand for you to carry out.” All you need is to employ your mouth and your heart.