רַבִּי יַעֲקֹב הִיא דְּאָמַר שְׂכַר מִצְוָה בְּהַאי עָלְמָא לֵיכָּא
Rabbi Ya’akov, who says: There is no reward for performance of a mitzva in this world, as one is rewarded for mitzvot only World-to-Come.
And it seems to explain we need to look into the teachings of the sages -
איתא במדרש כל מה שישראל אוכלים בעולם הזה אינם אוכלים אלא בשביל שכר האמונה.
As its taught in the Medrash, all of that with Israel eats and gets nourishment from, is only due to their reward for having faith.
abide in the land and remain loyal.
And behold, the essence of faith is that one believes in Divine Providence, that HaShem Yitbarach is looking over us on ALL matters. And with all ones might we place on HaShem all of our needs that He will oversee and guide, and whatever you do get in this world has been set aside for you since the time of the creation of the world.
And as is known in the story regarding the Baal Shem Tov, may his merit rest upon us. There was one time the Baal Shem was on a journey with his student somewhere in a desolate area, and the student was so parched for water until it became a matter of life and death, and he said - "Rabbi, I am parched enough that may soul may leave" and the Baal Shem Tov says back "Do you believe whole heartedly and with a pure heart, that the second that HaShem created the world, He saw you and your current situation, and has already prepared for you water to drink in this desolate area?"The student did not answer back right away until his mind settled and let the question sink into his heart fully, and then he responded to the Baal Shem - "I do truly believe this".. they then walked a little more they saw a merchant who was carrying water on his shoulders, and when he came near to them they gave him some coin, and they were given what to drink. Afterwards the Baal Shem asked the merchant whats going on that he's in this desert with water? The merchant responded back - "My master went crazy, and had sent me to this one specific well to get water, and I've been walking miles already, and I have no clue why I am on this mission." The Baal Shem then said to his student, "Don't you see this divine providence?, a master was created to go insane, all to provide for you water, and all of this HaShem saw during the time of the Creation, when everything was created, and since then has been watching over you with divine providence, to worry on your behalf to quench your thirst.
And when a person instills inside of himself faith in divine providence, then he/she will upkeep what is commanded in the Holy Torah, to be pure before HaShem.
As we can see below that this is from the Torah, and Rashi sheds some light on what this really means.
תָּמִ֣ים תִּֽהְיֶ֔ה עִ֖ם יְהֹוָ֥ה אֱלֹהֶֽיךָ׃
(ויקרא כה, נג) כשכיר שנה בשנה שכירות של שנה זו אינה משתלמת אלא בשנה אחרת:
“Like a hired laborer, year by year” (Leviticus 25:53). It is derived from this verse that the obligation to pay the rental fee of this year is incurred only in the following year.
And its common to be taught by the sages - "We are only nourished through the power of faith"
(4) Lo, his spirit within him is puffed up, not upright, But the righteous man is rewarded with life for his faith.
However based on our words above that faith can bring you reward in this world, since there is no aspect of being bound by a job that has an end, since faith is endless - it would seem then the answer is based on having faith one can receive what they need while on the planet. And this is why the above verse says that 'A righteous person will live by faith", that even though this person is a Tzaddik, righteous, and is fulfilling all the is required while down here, and has reward seeded for the future, but if he wants to have a life of nourishment while down here, then the only path is through faith! Because without faith, what would a person use to justify the request payment prior to completing his/her days!
And on this we will say a new thing - and let us look in the writings of the Degel Machane Efrayim in the name of our elder the Holy Baal Tov, may his merit rest upon us that teaches - "The main principal of the Torah and Mitzvot depends on faith"
And similarly it is written -
(86) All Your commandments are faith; Falsehood is chasing after me; help me!
And with this we can perfectly explain the opening verse of getting reward in this world and the contradiction we discussed. Which is that one keeps all of the Commandments as a decree without needing to know the reasons, which means that someone is simply keeping the Torah do to simple faith, and through this, someone can actually receive all of the rewards of the Torah in this world, and HaShem will provide for him/her expanded nourishment and resources with ease, since they are at a level of getting their reward while still alive.
And this is why the verse says "I will provide for them their rains", in plural, in Hebrew the word for rain can also be for material possessions, (Geshem, Gashmiut), which rain is referring to your lively-hood as well, which will be given in 'its time', which is the time that you are alive on this planet, due to the reality of having faith brings direct nourishment, even in this world.