The one God, the Supreme Being, is the Father in particular. “Yet for us there is but one God, the Father, from whom are all things and we exist for Him; and one Lord, Jesus Christ, by whom are all things, and we exist through Him.” 1 Cor 8:6 NASB. However, these are many who, acknowledging only one Supreme Being, the one God, wish to say that this one God is not the Father alone and in particular, as the scriptures teach, but the persons of the Son and Spirit as well. As a person is a rational individual being by definition, the concept of a multipersonal being is a logical impossibility. However, many have sought to redefine the very term ‘person’ itself, as merely a mode of subsistence or consciousness, and argued that it is possible to have three such “persons” in a single individual being. The following arguments refute that notion by proving that the Supreme Being is not the Father and the Son, but the Father alone, regardless of how ‘person’ is defined.
Proof #1: The Supreme Being, the One God, is uncaused. The Son, as having been begotten from the Father before creation, is caused. Therefore, the Son is not the Supreme Being.
Proof #2: The Supreme Being, the One God, is absolutely sovereign over all; all things are subject to Him as being under His dominion, and He Himself is subject to none, under the dominion and authority of none. The Son is subject to the Father, being under His authority and serving Him as His God. Therefore, the Son cannot be the Supreme Being.
Proof #3: The Supreme Being, the One God, is invisible to mortal man. The Son, on the other hand, was seen my mortal man in His own person both before and after His incarnation, and so, is visible. Therefore, the Son is not the Supreme Being.
Proof #4: A mediator between a being and another party cannot be that same being; and so must be a distinct individual being. The Son of God is the one Mediator between God and man. Therefore the Son is necessarily a distinct individual being from the one God, or else He could not be Mediator.
Proof #5: A son is always a distinct person from his father. Therefore, if Christ is the Son of the Father, He cannot be the same person, and the persons of Father and Son cannot be one and the same. Therefore the Father and Son cannot be the same individual being. For if They are each only part of the Supreme Being, then neither is the Supreme Being, but each is only a part of it; but if each is equal to the whole Supreme Being, then They will be identical in person as well as being. This can be demonstrated as follows (F=Father, S=Son, G=Supreme Being); If F=G, and S=G, then necessarily, F=S. Therefore, it is impossible, if Christ is the Son of God, that He be the same individual being as the Father.
While the above arguments pertain to the Son and not directly to the Holy Spirit, the same logic of the 5th proof holds good for the Holy Spirit as well, if He be admitted to be a distinct person from the Father (see that demonstrated here). And the 4th argument will also have some application to the Spirit, as He assists us in our prayers to God, we are told. Therefore, the Supreme Being, the One God, is the Father alone, not the Father, Son, and Holy Spirit together. And so the Son and Spirit are two distinct individual beings besides the one God, being His Son, and His Spirit.
For sake of brevity and clarity, I did not seek to support the premises of proofs above, but do so below. The conclusions of the above proofs necessarily follow, if the premises hold true.
Proof #1, expanded upon: That the One God, the Supreme Being, is the one uncaused Cause of all else, is the first point of natural theology, and assumed everywhere in the scriptures. And that “the Father is greater than all” confirms this clearly enough; for if the Father were caused, undoubtedly the one Who caused Him would be greater than Him. That the Son is begotten from the Father has been the most central point of trinitarian doctrine since the 2nd century. It is affirmed in scripture as a necessary deduction from many passages in John, which at once teach that the Son is begotten, and has His life from the Father, and yet, that He was already with the Father and lived with Him before all creation and all time. The Son’s generation then must have taken place before time. “For just as the Father has life in Himself, even so He gave to the Son also to have life in Himself;” John 5:26 NASB. Proverbs 8:22-31 is also clear in teaching this, and was so taken by nearly the entire early church, and on all sides of the Arian controversy.
Proof #2, expanded upon: That the Supreme Being rules over all absolutely is also a point of natural theology, understood even by the heathen. And so Paul proclaimed nothing novel to the Athenians when he said “The God who made the world and all things in it, since He is Lord of heaven and earth, does not dwell in temples made with hands; 25 nor is He served by human hands, as though He needed anything, since He Himself gives to all people life and breath and all things; 26 and He made from one man every nation of mankind to live on all the face of the earth, having determined their appointed times and the boundaries of their habitation, 27 that they would seek God, if perhaps they might grope for Him and find Him, though He is not far from each one of us;” Acts 17:22-27 NASB. Since God is the cause of all else that exists besides Himself, it follows and is fitting that He has dominion over all that He has caused. And that God rules over all absolutely is declared by scripture when He is said many times to be “Almighty”, which is the Greek word Pantokrator, literally, Ruler over all, or Supreme Ruler. And this is not said of God in a qualified way, so as to exclude the Son and Spirit from being under His authority, but is said absolutely, without qualification, and so not only all creation, but also the Son and Spirit, are subject to the Father. That God is the head of Christ (1 Cor 11:3) is repeatedly taught in the scriptures. “But when He says, “All things are put in subjection,” it is evident that He is excepted who put all things in subjection to Him. 28 When all things are subjected to Him [the Son], then the Son Himself also will be subjected to the One who subjected all things to Him, so that God may be all in all.” 1 Cor 15:27-28 NASB. The Son’s subjection to the Father is also seen throughout the OT, where He obeyed the Father in creating the world according to His command, and served as His Angel, that is, Messenger, to the men of old. And so being sent by the Father, He is clearly subject to Him, in the obedience of filial love.
Proof #3, expanded upon: God’s invisibility to mortal man, it is clearly stated in scripture more than a few times: “But He said, “You cannot see My face, for no man can see Me and live!”” Ex 33:20 NASB “No one has seen God at any time; the only begotten God who is in the bosom of the Father, He has explained Him.” John 1:18 NASB “Not that anyone has seen the Father, except the One who is from God; He has seen the Father.” John 6:46 NASB “No one has seen God at any time; if we love one another, God abides in us, and His love is perfected in us.” 1 John 4:12 NASB “He is the image of the invisible God, the firstborn of all creation.” Col 1:15 NASB “Now to the King eternal, immortal, invisible, the only God, be honor and glory forever and ever. Amen.” 1 Tim 1:17 NASB. But one may object, ‘Was not the Father seen, in Revelation, and in Daniel?’ It is best understood this way, that the Father has never been, and cannot be, seen in His own person by mortal man (whereas the Son can be and was); but can be ‘seen’ figuratively under symbols as in Revelation and Daniel, because what was seen was not the Father in His own person but a mere symbol (for God is not a man sitting on a throne, and the Son is not a fluffy animal with a bunch of eyes and horns; they are mere symbols). So while the Supreme Being, the one God, cannot be seen by mortal man in His own person, the Son was, from the beginning. For Adam hid from God walking in the garden; and God closed the Ark behind Noah; spoke face to face with Abraham, and wrestled with Jacob. And Isaiah saw His glory (Jn 12:41). This was not the Father Who was seen, for as has been shown above, that is impossible; but rather was the Son, for this God Who appeared to the men of old is no mere created angel, but bears the very name LORD, which we are not told that God has shared with any other, besides His only-begotten Son.
Proof #4, expanded upon: “For there is one God, and one mediator also between God and men, the man Christ Jesus,” 1 Tim 2:5 NASB. “Now a mediator is not for one party only; whereas God is only one.” Gal 3:20 NASB. The mediator, then, not being for one party only, all the more cannot be one of the parties between whom there is mediation.
Proof #5, expanded upon: That Christ is the Son of God is among the most plain and central teachings of scripture: “Simon Peter answered, “You are the Christ, the Son of the living God.” Matt 16:16, NASB. “If we receive the witness of men, the witness of God is greater; for this is the witness of God which He has testified of His Son. 10 He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son. 11 And this is the testimony: that God has given us eternal life, and this life is in His Son. 12 He who has the Son has life; he who does not have the Son of God does not have life.” 1 John 5:9-12 NKJV. That the Son and Father are not the same person is obvious, but made even more explicit in these passages, among others: “Jesus answered and said to him, “If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our home with him.” John 14:23 NASB. The Lord could not have said “We”, but must rather have said “I”, if He and His Father were not two distinct persons. “If I bear witness of Myself, My witness is not true. 32 There is another who bears witness of Me, and I know that the witness which He witnesses of Me is true… the Father Himself, who sent Me, has testified of Me. You have neither heard His voice at any time, nor seen His form.” John 5:31-32, 37 NKJV. The Father cannot be “another witness” unless he is another person, distinct from the Son.