Some important implications grow out of the fact of the unity of God, implications that in the very nature of the case are self-evident.
1 . In the area of logic, it is absolutely self-contradictory to entertain the notion of two or more gods. The existence of more than one God poses a situation in which each limits the other and thus destroys godhood. Infinity and absolute perfection cannot be possessed by more than one. It follows then that dualism is a clear impossibility, tri-theism increases the impossibility, and polytheism becomes a logical monstrosity. "Henotheism [that is, one god among many---explanation mine] conceives of each individual god as unlimited by the power of other gods. Each is felt, at the time, as supreme and absolute, notwithstanding the limitations which to our minds must arise from his power being conditioned by the power of all the gods!"
2. In the area of philosophy, the attempt to articulate the idea of many gods into the whole of reality, when one God will satisfactorily explain everything, is ludicrous. Tennyson intuited this fact in his poem, In Memoriam:
"That God who ever lives and loves,
One God, one law, one element,
And one far off divine event
To which the whole creation moves."
But the unity of God, from the philosophical standpoint, is in no way inconsistent with the doctrine of the Trinity. While the doctrine of the Trinity holds to the existence of three distinct persons in the Godhead, these distinctions are not to be confused with the doctrine of unity which holds that the divine nature is numerically and eternally one.
3. In the area of science, the very constitution of the universe depends upon the existence of one God. The unity of God has given order to creation, so that there is a universe and not a multiverse. It is this Fact that has furnished the impulse for research in every area of the created order. Whether looking through the telescope into the far reaches of the universe, or through the microscope into the area of the infinitesimal, a sublime and majestic order has been discovered, and this order moves over one pattern directed by a God who is one. It is this metaphysical basis out of which scientific exploration has grown. And it was upon the basis of this fact that in the beginning God issued the command to men to subdue the earth (Gen. 1:28).
4. In the area of religion, the unity of God alone provides the dynamic for exclusive devotion to one God. The doctrine of the unity of God should make it perfectly clear that there is no hope of finding any other deity to whom men owe responsibility and devotion. Since there is just one God, then He is the God of all men, Jews and Gentiles, and there is just one way or salvation (Rom. 3:29-30). To this one God men are responsible to give glory to (1 Pet. 4:11), whatever their activities may be (1 Cor. 10:31), understanding that God will not give His glory to another (Isa. 48:11). Men are in the hands of one God, so there is only one law, one gospel, one salvation, one doctrine, one duty, one destiny.
5. In the area of the practical, the unity of God provides the only basis for undivided allegiance and an inflexible morality. It will be seen by a close examination of Deut. 6:4-5 that there is a connection between the unity of God and love for God. "Hear, 0 Israel: The Lord our God is one Lord. And thou shalt love the Lord thy God with all thine heart, and with all thy soul, and with all thy might." This undivided, undiminished, unabated energy of the human heart can be directed to one God, whereas it would be impossible if there were more than one God. Polytheism was an attempt on the part of man to escape the notion of moral responsibility to one moral Lawgiver and Judge by dividing his allegiance to separate wills. The result was the tragic retreat into darkness and the awful descent into immorality and the lowest forms of sensuality (Rom. 1:19-31).
The only way of salvation centers in the unity of God. Isaiah insists that a carved image of wood cannot save (Isa. 45:20). He strengthens his argument by reference to the unity of God. "And there is no God else beside me, a just God and a Savior: there is none beside me" (Isa. 45:21). Upon this basis the invitation goes forth. "Look unto me, and be saved, all the ends of the earth; for I am God, and there is none else" (Isa. 45:22).
On the basis of the unity of God, James argues for the unity of the law (James 2:9-11). It was the one and same God who gave it all. Therefore, no one who claims to be a worshipper of God can observe some of it and ignore other parts. If a man breaks one law, he has become guilty of all, because he has defied the one God who gave it all. Any portion he keeps will be for some other reason than obedience to the one God.