Benedict Pictet, Swiss Reformed divine (May 30, 1655 — June 10, 1724) and nephew of Francis Turretin.
“In the preceding chapters we set forth the unity of God, and his principal attributes; we must now observe that the scripture expressly mentions three persons to whom the divine nature is ascribed, namely, the Father, the Son, and the Holy Ghost. Of these three the scripture speaks unitedly in various places; for not to mention the baptism of Christ, in which the Father revealed himself by the voice that was heard; the Son, who was the subject of the divine oracle, was seen; and the Holy Ghost descended in the shape of a dove; the following passages are well know: “Go ye, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost.” (Matt. xxxviii. 19.) “The grace of our Lord Jesus Christ, and the love of all.” (2 Cor. xiii. 14.) See also John xiv. 16; 1 Cor. Xii. 3; Gal. iv. 6. So also in Rev. i. 4, 5, John seeks grace “from him which is, and which was, and which is to come,” namely, from the Holy Ghost, (so called on account of his manifold gifts, and with an allusion also to the seven churches of Asia,) and “from Jesus Christ, the faithful witness, &c.” And not only in the New Testament is there mention made of these three unitedly, but in the Old Testament also. “I will mention the loving-kindness of the Lord, &c., for he said, Surely they are my people,” &c., (this is said of the Father.) The Angel of his presence saved them; in his love and in his pity he redeemed them, &c., (this concerning the Son.) But they rebelled, and vexed his Holy Spirit, (this concerning the Spirit.) (Isaiah lxiii. 7-10.) “The Spirit of the Lord God is upon me (the Son), because the Lord hath anointed me (by his Spirit) to preach the gospel to the poor.” (Isaiah lxi. 1.) Nor must we omit those passages in which the plurality of persons appears to be pointed out, such as “Let us make man in our image.” “Behold the man is become as one of us.” “Go to, let us go down, and confound their language.” (Gen. xi. 7.)
Concerning these three persons we must remark, that they are distinct from each other, as is evident from the passages already quoted, and many others; thus Psalm cx. 1, “The Lord said unto my Lord, Sit thou at my right hand.” Here the Lord who speaks is distinguished from the Lord who is spoken to. So also John xv. 26, “When the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me.” Here the Comforter, or Spirit, is plainly distinct from the Father and the Son. Against, they are so distinguished, that some things are said of the Father which cannot be said of the Son, and some things of the Son which are no where said of the Spirit. The Father is said to have begotten the Son but the Son is no where said to send the Father. The Spirit is said to proceed from the Father, and to be sent by the Son; but no where is the Father said to proceed from, nor the Son to be sent by, the Spirit. Yet are these persons distinct in such a manner, that they are not three Gods but one God; for the scripture every where proves, and reason confirms, the unity of the Godhead. There are, therefore, three persons in one divine essence; and this is clearly established by the passage in 1 John v. 7, which is brought forward and quoted by Cyprian, although not read in many copies. A far greater number of reasons can be alleged why this passage should have been inserted by the orthodox. It was more to the advantage of heretics to suppress this passage, than to that of the orthodox to add it, because, if it were genuine, the heresy of the former would be entirely overthrown; if spurious the orthodox creed was in no danger, being clearly established from other passages of scripture. The connection also of the text confirms our opinion; for unless this verse be admitted, there seems no reason why John should say, “There are three that bear witness in earth,” not having before said any thing of “three witnesses in heaven.” Nor can it be objected that these words in earth, were also added afterwards, for the contrary appears from verse 9, where mention is made both of the divine and human testimony, “If we receive the witness of men, the witness of God is greater.”
This mystery of three in one, is called the mystery of the Trinity, a word not expressly written in the scriptures, but wisely invented, and advantageously used, for the purpose of exposing the shifts and subterfuges of crafty heretics, just as other words have been invented and used, such as … (of the same essence), … (essence), … (subsistence), &c. Concerning this mystery we must inquire soberly, and speak modestly, since the human mind cannot conceive, nor mortal tongue express, the greatness of it; and, therefore, we can have nothing to do with the unbridled audacity of the vain and speculating schoolmen, who, by their plausible and dangerous subtleties, have given room for the introduction of various heresies. We may examine things revealed, but not rashly pry into secret things, lest as Prosper remarks, we should be convicted of unlawful curiosity in the latter, and of blamable negligence in the former. Distinguished men, both in this and former ages, have attempted to render this mystery plain by many examples. I admire their ingenuity, united as it is with an ardent desire for the promotion of Christian truth; while I read what they have written, my mind is captivated both by their ingenuity and by their eloquence are removed and the mind is brought down to a little closer consideration of the subject, all that they have advanced is, in a great measure, forgotten. But although this mystery is incomprehensible to mortals, it must be rejected by us for it is not strange that finite beings, such as we are, should not perfectly comprehend the nature of an infinite Being. It is enough to have proved from the scriptures these two points, that there is one God, and that the Godhead is ascribed to three persons, distinct from each other. The latter we have begun to prove, and shall prove still further. But to assist our understanding on this subject, we may observe that the divine essence is infinite; also, that we do not comprehend how this essence is common to three persons, for this reason, — because we judge of the divine essence as we do of a finite essence, which cannot subsist in more than one. Further, that the divine essence subsisting in a plurality of persons, arises from the Infinite nature of Deity, but that these persons are no more than three, is only known from revelation. Gregory Nazianzen excellently remarks on this subject, I cannot attempt to think of one, but I am instantly surrounded with the splendor of three; I cannot attempt to distribute the three, but I am instantly carried back to the idea of one. These three, in whom the divine essence subsists, are called persons, which is the term we shall make use of in the ensuing pages; we confess, indeed, that it is not so appropriate, but for want of other terms, we are compelled to adopt this, in common with the whole Christian church.”
Benedict Pictet, Theologia Christiana, Book 2 Ch. 9 (Of the Trinity), 1696