Psalms 81:9

9Let there be no strange god (414) in thee. Here there is propounded the leading article of the covenant, and almost the whole sum of it, which is, that God alone must have the pre-eminence. Some may prefer this explanation: O Israel! if thou wilt hearken to me, there is nothing which I more strictly require or demand from thee than that thou shouldst be contented with me alone, and that thou shouldst not seek after strange gods: and of this opinion I am far from disapproving. God by this language undoubtedly confirms the truth which he so frequently inculcates elsewhere in the law and the prophets, that he is so jealous a God as not to allow another to be a partaker of the honor to which he alone is entitled. But at the same time he teaches us that true religious worship begins with obedience. The order which Moses observes is different, Exodus 20:2, and Deuteronomy 5:6. In these passages God sets out with declaring that he is the God of Israel; and then he forbids them to make for themselves any new gods. But here the prohibition is put first, and then the reason of it is subjoined, which is, that the people ought to be abundantly satisfied with the God who had purchased them to be his people. Perhaps also he sets this in the front to prepare the way for his obtaining the throne of their hearts. He would first withdraw the people from superstitions, as these must necessarily be plucked up and cleared away before true religion can take root in our hearts.