The whole mitzvah

(1) You shall faithfully observe all the Instruction that I enjoin upon you today, that you may thrive and increase and be able to possess the land that ה׳ promised on oath to your fathers.

All the commandments which I command thee this day shall you observe to do, that you may live, and multiply, and go in and possess the land which the Lord swore to your fathers. Koren

(22) If, then, you faithfully keep all this Instruction that I command you, loving your God ה׳, walking in all God’s ways, and holding fast to [God],

(25) It will be therefore to our merit before our God ה׳ to observe faithfully this whole Instruction, as [God] has commanded us.”

§ Rabbi Simlai taught: There were 613 mitzvot stated to Moses in the Torah, consisting of 365 prohibitions corresponding to the number of days in the solar year, and 248 positive mitzvot corresponding to the number of a person’s limbs. Rav Hamnuna said: What is the verse that alludes to this? It is written: “Moses commanded to us the Torah, an inheritance of the congregation of Jacob” (Deuteronomy 33:4). The word Torah, in terms of its numerical value [gimatriyya], is 611, the number of mitzvot that were received and taught by Moses our teacher. In addition, there are two mitzvot: “I am the Lord your God” and: “You shall have no other gods” (Exodus 20:2, 3), the first two of the Ten Commandments, that we heard from the mouth of the Almighty, for a total of 613.

It is among the fundamental principles of the Torah that when an individual fulfills one of the 613 commandments in a fit and proper manner, not combining with it any aspect of worldly intent but rather doing it for its own sake, out of love, then they merit the World to Come through this single act. This is what R' Hananya meant - being that the Holy One have us so many commandments it is impossible that in a lifetime one not do a single one in a full and proper manner, and in doing so their soul will live through that act. When R' Hananya ben Tradiyon's asked 'will I merit to life in the coming world' and received the response 'have you ever done anything?' this also indicated the same principle. The answer he received meant 'have you ever had the chance to do one of the commandments properly?' His answer was that he once had the chance to give tzedaka in a wholehearted fashion, as much as is possible, and it was through this that he merited to life in the World to Come.

Another interpretation: "All of the commandment" (Deuteronomy 8:1). If you have began with a commandment, finish all of it. Why? Rabbi Yochanan said, "Anyone who began with a commandment, and afterwards another comes and finishes it, it will be called according to the name of the one who finishes it."

... Rabbi Yochanan said, "Anyone who learns Torah but does not fulfill it, it is better for him to have his placenta roll over his face [and smother him], as it is stated (Deuteronomy 8:1), 'guard to keep.'"

כל המצוה אשר אנכי מצוך היום, “the whole (set) of commandments which I command you this day, etc.;” The placing in apposition of the words כל המצוה, to the paragraph teaching us how we are to relate to paganism is meant to convey that he who takes the instructions of the previous chapter to heart is considered as if he had fulfilled כל המצוה, “all the commandments.” Our sages reinforced this when they said anyone who denies paganism is as if he had expressly acknowledged the entire Torah; conversely, if someone acknowledges any aspect of idolatry as true he is considered as if he had denied the totality of Torah and Judaism.

We find the following comment in Devarim Rabbah (Lieberman edition Nitzavim page 14): the words כל המצוה are to be understood as “fulfill the commandment to its nth degree, completely;” the author means that if you have commenced to fulfill a certain commandment make every effort to complete that commandment. Do not content yourself with half-measures. (compare also Tanchuma Eykev 6) where the Midrash states that the credit for fulfilling a commandment goes to the person who completes it.

Another matter, what is written prior to this passage? “For if you will observe [this entire commandment]” (Deuteronomy 11:22). What is “this entire commandment”? Rabbi Levi said: This is the recitation of Shema. The Rabbis say: This is Shabbat, which is equivalent to all the mitzvot in the Torah.

What the verse said: “For they are life for those who find them…” (Proverbs 4:22) – ...

Alternatively, “for they are life for those who find them [motzeihem]” – for one who completes [shemamtzi] all the mitzvot. From where is it derived? It is as it is stated: “All the mitzva” (Deuteronomy 8:1). What is “all the mitzva”? It is until you complete all the mitzvot. "And an elixir for your bones” (Proverbs 3:8), the 248 limbs that you have. That is "For this mitzva."

The Midrash Tanchuma (Eikev 5:1) explains “All of the commandment that I command you today” (Devarim 8:1) by linking it to Mishlei 4:22, “They (the words of Torah) are life to him who finds them.” The word למוצאיהם (finds them) can be read as למוציאהם (expresses them), meaning Torah must be verbalized, not just understood. Additionally, “All of the commandment” teaches that one must complete a mitzvah, as it is credited to the finisher.
The life force of everything comes from Torah and mitzvos. More toil in Torah brings more life force, connecting one to the source of life. Mishlei 7:1, “Keep my mitzvos with you,” means each mitzvah leaves a bit of closeness to Hashem.

Perform mitzvos not out of habit, but with connection to their inner part.
“All the commandment” (Devarim 8:1) implies extracting maximum gain from a mitzvah by accessing its inner energy.

Devarim 11:13, “You shall hear תשמעו my commandments,” suggests mitzvos produce a sound. Each mitzvah is connected to a specific limb and reminds the person to perform it. However, the mitzvah’s voice is heard in proportion to one’s desire to connect to its inner part.

And may [this] commandment of tsitsit be considered before the Holy One, blessed be He, as if I fulfilled it in all of its details, all of its minutiae and all of its intentions – [as well as] the 613 commandments that are dependent upon it. Amen, Selah.