John Owen Works Vol 12 pp. 72ff.
By the subsisting of God in any person, no more is intended than that person’s being God. If that person be God, God subsists in that person. If you grant the Father to be a person (as the Holy Ghost expressly affirms him to be, Hebrews 1:3) and to be God, you grant God to subsist in that person: that is all which by that expression is intended. The Son is God, or is not. To say he is not God, is to beg that which cannot be proved. If he be God, he is the Father, or he is another person. If he be the Father, he is not the Son. That he is the Son and not the Son is sufficiently contradictory. If he be not the Father, as was said, and yet be God, he may have the same nature and substance with the Father (for of our God there is but one essence, nature, or being), and yet be distinct from him. That distinction from him is his personality, — that property whereby and from whence he is the Son. The like is to be said of the Holy Ghost. The thing, then, here denied is, that the Son is God, or that the Holy Ghost is God: for if they are so, God must subsist in three persons; of which more afterward.
The eternal generation of the Son is in the next place rejected, that he may be sure to cast down every thing that looks towards the assertion of his deity, whom yet the apostle affirms to be” God blessed for ever,” Romans 9:5.
That the Word, which “in the beginning was” (and therefore is) “God,” is “the only begotten of the Father,” the apostle affirms, John 1:14. That he is also” the only begotten Son of God” we have other plentiful testimonies, Psalm 2:7; John 3:16; Acts 13:33; Hebrews 1:4-6; — a Son so as, in comparison of his sonship, the best of sons by adoption are servants, Hebrews 3:5, 6; and so begotten as to be an only Son, John 1:14; though, begotten by grace, God hath many sons, James 1:18. Christ, then, being begotten of the Father, hath his generation of the Father; for these are the very same things in words of a diverse sound. The only question here is, whether the Son have the generation so often spoken of from eternity or in time, — whether it be an eternal or a temporal generation from whence he is so said to be “begotten.” As Christ is a Son, so by him the “worlds were made,” Hebrews 1:2, so that surely he had his sonship before he took flesh in the fullness of time; and when he had his sonship he had his generation. He is such a Son as, by being partaker of that name, he is exalted above angels, Hebrews 1:5; and he is the “first begotten” before he is brought into the world, verse 6: and therefore his “goings forth” are said to be “from the days of eternity,” Micah 5:2; and he had glory with the Father” (as the Son) “before the world was,” John 17:5. Neither is he said to be “begotten of the Father” in respect of his incarnation, but conceived by the Holy Ghost, or formed in the womb by him, of the substance of his mother; nor is he thence called the “Son of God.” In brief, if Christ be the eternal Son of God, Mr B. will not deny him to have had an eternal generation: if he be not, a generation must be found out for him suitable to the sonship which he hath; of which abomination in its proper place.