'וזכרת את ה', "You shall remember the Lord your God." He alone is the source of your good fortune because He has given you the strength to perform deeds of valour. In other words: "He handed over to you the power to overcome negative horoscopic influences, influences which God had created to perform His will in the terrestrial regions. None of these constellations have any power or influence over you and your fate. This is what our sages meant when they said אין מזל לישראל, "Israel is not subject to horoscopic influences"
(Shabbat 156). This is also meaning of the end of our verse: "in order to maintain His covenant which He swore to your forefathers as of this day." God, in His first appearance to Avraham, had positioned him above the stars, making him look down at the stars to teach him that his descendants' fate would not be governed by such stellar constellations.
(Compare Genesis 15,5 and Bereshit Rabbah 44,14 on that verse).
The expression הבט in that verse always implies "looking down on something."
Although, technically, the wording there is in the singular, whatever God said to Avraham at the time was intended to cover the Jewish people as a whole not just the individual fate of Avraham. Our paragraph also commences with the singular but continues by using the plural אשר תשמרון לעשות.
You might argue that Moses addressed every single Israelite making his message relevant for all future generations and this accounts for the address in the singular, and the meaning of the verse would be: "if you will say in your heart that the wealth and affluence have been decreed from heaven for each Israelite individually rather than for the people collectively." You would base this on the saying that: "there are no horoscopic forces which determine the fate of the Israelites collectively, though there are such forces at work determining the individual fate of the nation." You might cite the statement that "economic success, the ability to have children, and the control over life and death do not depend on individual merit but on mazzal"
(Moed Katan 28). This consideration might prompt you to ascribe your success to כחי "my personal mazzal." In fact you would ascribe your success to a combination of the forces at work in outer space and those beneath the earth; Moses tells you here that you must not commit such an error but you must "individually remember (וזכרת את ה' אלו-היך), the Lord your God," i.e. He gave you individually the strength to accomplish what you thought was decreed for you by the stars. Whereas God may have used intermediaries to channel success your way, were it not for the power He personally equipped you with, all the stars in the world would not have the power to influence your well being by one iota.
This is what Solomon had in mind when he said in Proverbs 22,2: "Rich man and poor man meet; the Lord made them both." He meant that success and failure are occurrences; they encounter each other due to the motions of the planets in orbit, not because the people who appear to possess it have acquired it due to their superior intelligence or have failed to acquire it due to their inferior intelligence. Neither is the reason for acquisition of wealth due to more sustained effort by one party than the other. Having assimilated this lesson you might say that seeing that success is not due to effort why make any effort at all? It is all the doing of the horoscopic constellations!" To ensure that you do not reason in this fashion Solomon added: "the Lord makes them both." Everything is the result of Divine decree, even if it sometimes appears as if it is accidental or due to independent power residing in stellar forces.