Sforno on Deuteronomy 4:39/ספורנו על דברים ד׳:ל״ט

1וידעת היום, it behooves you therefore to understand how these miracles confound any theological theories that are not in agreement with Jewish tradition.

2והשבות אל לבבך, having carefully examined all these factors you are to establish firmly in your heart which is the truth, namely כי ה' הוא האלוקים, that the Lord known to us as Hashem is the true G’d, the word itself indicating that He is victorious in any competition who make similar claims because He is eternal. His fame extends both בשמים, in the celestial spheres above, as well as על הארץ מתחת, for you will realise that the very order which exists among celestial phenomena, their predictability to the second, is proof that Someone is guiding them, has programmed them.

3אין עוד. You will also realise that it is quite inconceivable that there could be more than One such supreme authority over all these phenomena. Among disembodied spiritual forces it is quite impossible for two such forces to co-exist as equals. One such force, power, must be superior to the other.