Below is some Preliminary Remarks of Charles Hodge about the Trinity from his writings about Systematic Theology - Volume I: There are many options below to download: or go to the following link to access this information there: http://www.ccel.org/ccel/hodge/theology1.html
Systematic Theology - Volume I
Hodge, Charles (1797-1878)
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§ 1. Preliminary Remarks.
THE doctrine of the Trinity is peculiar to the religion of the Bible. The Triad of the ancient world is only a philosophical statement of the pantheistic theory which underlies all the religion of antiquity. With the Hindus, simple, undeveloped, primal being, without consciousness or attributes, is called Brahm. This being, as unfolding itself in the actual world, is Vishnu; as returning into the abyss of unconscious being, it is Shiva. In Buddhism we find essentially the same ideas, in a more dualistic form. Buddhism makes more of a distinction between God, as the spiritual principle of all things, and nature. The soul of man is a part, or an existence-form, of this spiritual essence, whose destiny is, that it may be freed from nature and lost in the infinite unknown. In Platonism, also, we find a notional Trinity. Simple being (τὸ ὀν) has its λόγος, the complex of its ideas, the reality in all that is phenomenal and changing. In all these systems, whether ancient or modern, there is a Thesis, Antithesis, and Synthesis; the Infinite becomes finite, and the finite returns to the Infinite. It is obvious, therefore, that these trinitarian formulas have no analogy with the Scriptural doctrine of the Trinity, and serve neither to explain nor to confirm it.
The design of all the revelations contained in the Word of God is the salvation of men. Truth is in order to holiness. God does not make known his being and attributes to teach men science, but to bring them to the saving knowledge of Himself. The doctrines of the Bible are, therefore, intimately connected with religion, or the life of God in the soul. They determine the religious experience of believers, and are presupposed in that experience. This is specially true of the doctrine of the Trinity. It is a great mistake to regard that doctrine as a mere speculative or abstract truth, concerning the constitution of the Godhead, with which we have no practical concern, or which we are required to believe simply because it is revealed. On the contrary, it underlies the whole plan of salvation, and determines the character of the religion (in 443the subjective sense of that word) of all true Christians. It is the unconscious, or unformed faith, even of those of God’s people who are unable to understand the term by which it is expressed. They all believe in God, the Creator and Preserver against whom they have sinned, whose justice they know they cannot satisfy, and whose image they cannot restore to their apostate nature. They therefore, as of necessity, believe in a divine Redeemer and a divine Sanctifier. They have, as it were, the factors of the doctrine of the Trinity in their own religious convictions. No mere speculative doctrine, especially no doctrine so mysterious and so out of analogy with all other objects of human knowledge, as that of the Trinity, could ever have held the abiding control over the faith of the Church, which this doctrine has maintained. It is not, therefore, by any arbitrary decision, nor from any bigoted adherence to hereditary beliefs, that the Church has always refused to recognize as Christians those who reject this doctrine. This judgment is only the expression of the deep conviction that Antitrinitarians must adopt a radically and practically different system of religion from that on which the Church builds her hopes. It is not too much to say with Meyer,473473Lehre von der Trinität , vol. i. p. 42.
that “the Trinity is the point in which all Christian ideas and interests unite; at once the beginning and the end of all insight into Christianity.”
This great article of the Christian faith may be regarded under three different aspects: (1.) The Biblical form of the doctrine. (2.) The ecclesiastical form, or the mode in which the statements of the Bible have been explained in the symbols of the Church and the writings of theologians. (3.) Its philosophical form, or the attempts which have been made to illustrate, or to prove, the doctrine on philosophical principles. It is only the doctrine as presented in the Bible, which binds the faith and conscience of the people of God.
The Holy Trinity
Lord’s Day 8
24. How are these articles divided?
Into three parts: the first is of God the Father and our creation; the second, of God the Son and our redemption; the third, of God the Holy Spirit and our sanctification.
 1 Pt 1:2
25. Since there is but one Divine Being, why do you speak of three persons: Father, Son, and Holy Spirit?
Because God has so revealed Himself in His Word,, that these three distinct persons are the one, true, eternal God.
 Deut 6:4; Isa 44:6, 45:5; 1 Cor 8:4-6;  Gen 1:2-3; Ps 110:1; Isa 61:1, 63:8-10; Mt 3:16-17, 28:18-19; Lk 4:18; Jn 14:26, 15:26; 2 Cor 13:14; Gal 4:6; Tit 3:5-6
Of God the Father and our CreationLord’s Day 9
26. What do you believe when you say: “I believe in God the Father Almighty, Maker of heaven and earth?”
That the eternal Father of our Lord Jesus Christ, who of nothing made heaven and earth with all that in them is, who likewise upholds, and governs the same by His eternal counsel and providence, is for the sake of Christ, His Son, my God and my Father, in whom I so trust as to have no doubt that He will provide me with all things necessary for body and soul; and further, that whatever evil He sends upon me in this troubled life, He will turn to my good; for He is able to do it, being Almighty God, and willing also, being a faithful Father.
 Gen 1-2; Ex 20:11; Job 38-39; Ps 33:6; Isa 44:24; Acts 4:24, 14:15; Col 1:16; Heb 11:3;  Ps 104:2-5, 27-30, 115:3; Mt 6:30, 10:29-30; Acts 17:24-25; Eph 1:11; Heb 1:3;  Mt 6:8; Jn 1:12-13; Rom 8:15-16; Gal 4:4-7; Eph 1:5, 3:14-16;  Ps 55:22, 90:1-2; Mt 6:25-26; Lk 12:22-31;  Acts 17:27-28; Rom 8:28;  Gen 18:14; Rom 8:31-39, 10:12;  Num 23:19; Mt 6:32-33, 7:9-11