One God does not simply mean that there is only one.
Verses 11 to 20 of Devarim chapter 8 deal with the dangers of forgetting God when things are good and the resultant danger of serving false gods. We are warned not to forget the Lord (verse 11), and we are told how this could happen: "Lest you eat and become satisfied, build good houses and settle…and all you have shall increase. And your heart shall be exalted and you shall forget the Lord your God who took you out of the land of Egypt…"(12-14). The enjoyable life that God gives us may turn us away from Him. Pleasures can make one vain and not wish to acknowledge the source of one's luxury.
But why would such a state of mind make one serve false gods? If one leaves the service of the true source of good, due to a conceited heart, exalted by luxury, why would one turn pagan? We would assume atheism a possible danger; but serving many gods instead of the One seems odd. Yet verse 19 explicitly continues the sequence: "It shall be, that if you do forget the Lord your God and you go after other gods, and serve them…I testify against you today that you shall perish." Since this verse is separated from the previous verses with a break in the original Hebrew text, one may claim that it is not a continuation. Verse 17 tells us that we may declare that it was our own strength that generated the success. We are then told in verse 18 that we must remember God, who gave us the strength to be successful. Since the text breaks at this point, one may argue that the subject has changed. However, a simpler reading would connect the two as stages in a terrible moral decline. First one becomes proud and forgets God. If one does not catch oneself, by remembering God who is the source of any strength to be successful, then a new stage of decline becomes possible: one may recede into a pagan mindset. According to this explanation, the break in the text does not separate the issues completely, but makes us aware that this is not a necessary continuation; the person would hopefully catch himself before he falls this far. I think that this explanation seems more plausible given the context of these verses. We must therefore ask ourselves why one who left the service of the one true God out of pride, not wanting to acknowledge the source of his success, would become pagan, and serve many gods.
This issue touches upon a fundamental difference between Monotheism and Paganism. One God does not simply mean that there is only one. It means that all power and meaning in the world emanates from Him. Everything in existence receives its life, strength and creativity from God; "You shall remember the Lord your God, for He is the one who gives you strength to beget wealth" (verse 18). Intoxicating pride in human achievement directly contradicts a truly monotheistic consciousness. However, Pagan thought works differently. In Greek mythology, for example, gods are remarkably human, and even in other cultures we may assume that a multiplicity of gods usually meant that one could weave one's way between them. Ritual to appease the gods was a way of dealing with powers which man wished to escape. When one does not believe in an all-powerful and all-encompassing God, the many gods that people believe in instead become players in the same field. The human being is considered weaker, but to some extent independent.
If one forgets God because of the pride that comes from prosperity, not wanting to attribute one's successes to God, one may indeed degenerate into pagan worship. Vanity and a conceited heart contradict belief in a monotheistic God; they do not contradict service of many powers in the world. The proud human being wants to believe in his absolute autonomy; he does not want to attribute his success to divine goodness, and belief in the one absolute source of everything deflates his pride. He turns to idols, as they present no challenge to his human vanity. Every generation has its own idols, and every human being his or her own pride. True belief in God saves one from the pride and from the idols.
Courtesy of Yeshivat Har Etzion - www.etzion.org.il