This means that having children, the length of one’s life, and the amount of wealth one receives are dependent not on one’s merits but on mazal. This comes to inform us how great is the power of tefillah, because since the power of Hashem is greater than all other powers, He can easily annul the great powers that He gave the mazalos. The expert astrologers look at the constellations, but they admit that Hashem is the ultimate Power, and the constellations are the secondary powers. Hashem can annul the powers of the stars and the constellations.
If mazal decreed that something should happen to someone, the person can annul it with his merits alone, even without tefillah and without crying out to Hashem, simply by worrying and being pained in his heart; as it says (Tehillim 145:19), “He does the desire of those who fear Him,” meaning that He carries out the wishes of their heart without their even asking; but in regard to those three things [i.e., children, life, and sustenance], one needs to daven and to cry out to Hashem in order to improve one’s measure of those things.
(Based on Rabbenu Bachyai al Hatorah, Devarim 31:14)
