At the beginning of each year, God grants each person his yearly portion of divine loving-kindness, but it remains on a high spiritual plane in the upper worlds. How that divine loving-kindness flows into his day-to-day existence in this temporal world is dependent on daily prayer.

Our [daily] prayers for health and sustenance and the like can be understood as follows: Even though [our yearly portion of sustenance] is fixed by God on Rosh HaShana and Yom Kippur, that divine decision only applies to the expression of divine loving-kindness in a general way, before it takes any concrete physical form. However, every day we request [in our prayers] that the loving-kindness set aside for us, and drawn from the highest spiritual levels, should take the concrete physical form [of good health and livelihood]. (Rabbi Shalom Dovber Schneersohn, Kuntres UMa’ayan 19:2)

Rabbi Levi Yitzĥak of Berditchev was once walking in the marketplace and saw a Jew wildly running through the streets, agitated.

I learned from my teachers, may God protect them, that anyone who is diligent about saying the blessing after a meal will be assured of having his livelihood provided for honorably for his entire life. (Sefer HaĤinnukh, Mitzva 430)

Even with the greatest exertion, it is impossible to earn even one penny more than the Holy One, blessed be He, set for how much an individual will earn [in a particular year]. One must do all that is necessary to earn a living. But one must remember that all of the work we do is only secondary to God’s blessing, may He be blessed, which is the main source of livelihood. We merit [such blessing] by acting as a Jew properly should. (Rabbi Yosef Yitzĥak Schneersohn, Hayom Yom, 4 Menaĥem Av)

Further reading: For more on trusting that God will supply all of a person’s needs, see p. 154.