The doctrine of the Trinity is not a product of councils or "ecclesiastical authority". It is revealed to us in the Scriptural record of redemption, and that not only in the New, but the Old Testament as well.
I do not need to use the word "philosophical" when talking of this, as though it were something which can either be apprehended or proved by mere human reason. It cannot. Thus I simply say with absolute certainty the doctrine of the Trinity is true.
The Lord knows His nature with absolute certainty, and He has used human language to convey what He knows to us. Language, when used by Him, can convey with absolute precision what He intends for us to understand. That the believing church is unanimous in its apprehension of what God has communicated regarding Himself in this matter reflects on His ability to have us do so.
The best treatment of this subject I've come across is Benjamin Warfield's essay,
"The Biblical Doctrine of the Trinity". In hard copy it is in P&R's
The B.B. Warfield Collection, the volume,
Biblical and Theological Studies, p. 22ff. It is also in the
ISBE, James Orr's edition, under "Trinity". Here is a sampling from it.
The term "Trinity" is not a Biblical term, and we are not using Biblical language when we define what is expressed by it as the doctrine that there is one only and true God, but in the unity of the Godhead there are three coeternal and coequal Persons, the same in substance but distinct in subsistence. A doctrine so defined can be spoken of as a Biblical doctrine only on the principle that the sense of Scripture is Scripture. And the definition of a Biblical doctrine in such unBiblical language can be justified only on the principle that it is better to preserve the truth of Scripture than the words of Scripture. The doctrine of the Trinity lies in Scripture in solution; when it is crystallized from its solvent it does not cease to be Scriptural, but only comes into clearer view. Or, to speak without figure, the doctrine of the Trinity is given to us in Scripture, not in formulated definition, but in fragmentary allusions; when we assembled the disjecta membra into their organic unity, we are not passing from Scripture, but entering more thoroughly into the meaning of Scripture. We may state the doctrine in technical terms, supplied by philosophical reflection; but the doctrine stated is a genuinely Scriptural doctrine.
In point of fact, the doctrine of the Trinity is purely a revealed doctrine. That is to say, it embodies a truth which has never been discovered, and is indiscoverable, by natural reason. With all his searching, man has not been able to find out for himself the deepest things of God. Accordingly, ethnic thought has never attained a Trinitarian conception of God, nor does any ethnic religion present in its representations of the Divine Being any analogy to the doctrine of the Trinity. (p. 22)
He then goes on to talk of triads of divinities in pagan religions, the failure of reason or philosophy to discover or prove the doctrine (he says Edwards perhaps comes the closest in his attempt), and its appearance in rudimentary form in the Old Testament. He says, "It is an old saying that what becomes patent in the New Testament was latent in the Old Testament. And it is important that the continuity of the revelation of God contained in the two Testaments should not be overlooked or obscured." (p. 30)
He then discusses the revelation given in the NT:
The simplicity and assurance with which the New Testament writers speak of God as a Trinity have, however, a further implication. If they betray no sense of novelty in so speaking of Him, this is undoubtedly in part because it was no longer a novelty so to speak of Him. It is clear, in other words, that, as we read the New Testament, we are not witnessing the birth of a new conception of God. What we meet with in its pages is a firmly established conception of God underlying and giving its tone to the whole fabric. It is not in a text here and there that the New Testament bears its testimony to the doctrine of the Trinity. The whole book is Trinitarian to the core; all its teaching is built on the assumption of the Trinity; and its allusions to the Trinity are frequent, cursory, easy and confident. It is with a view to the cursoriness of the allusions to it in the New Testament that it has been remarked that "the doctrine of the Trinity is not so much heard as overheard in the statements of Scripture." It would be more exact to say that it is not so much inculcated as presupposed. The doctrine of the Trinity does not appear in the New Testament in the making, but as already made. It takes its place in its pages, as Gunkel phrases it, with an air almost of complaint, already "in full completeness" (völlig fertig), leaving no trace of its growth. "There is nothing more wonderful in the history of human thought," says Sanday, with his eye on the appearance of the doctrine of the Trinity in the New Testament, "than the silent and imperceptible way in which this doctrine, to us so difficult, took its place without struggle - and without controversy - among accepted Christian truths." The explanation of this remarkable phenomenon is, however, simple. Our New Testament is not a record of the development of the doctrine or of its assimilation. It everywhere presupposes the doctrine as the fixed possession of the Christian community; and the process by which it became the possession of the Christian community lies behind the New Testament.
We cannot speak of the doctrine of the Trinity, therefore, if we study exactness of speech, as revealed in the New Testament, any more than we can speak of it as revealed in the Old Testament. The Old Testament was written before its revelation; the New Testament after it. The revelation itself was made not in word but in deed. It was made in the incarnation of God the Son, and the outpouring of God the Holy Spirit. The relation of the two Testaments to this revelation is in the one case that of preparation for it, and in the other that of product of it. The revelation itself is embodied just in Christ and the Holy Spirit. This is as much as to say that the revelation of the Trinity was incidental to, and the inevitable effect of, the accomplishment of redemption. It was in the coming of the Son of God in the likeness of sinful flesh to offer Himself a sacrifice for sin; and in the coming of the Holy Spirit to convict the world of sin, of righteousness and of judgment, that the Trinity of Persons in the Unity of the Godhead was once for all revealed to men. Those who knew God the Father, who loved them and gave His own Son to die for them; and the Lord Jesus Christ, who loved them and delivered Himself up an offering and sacrifice for them; and the Spirit of Grace, who loved them and dwelt within them a power not themselves, making for righteousness, knew the Triune God and could not think or speak of God otherwise than as triune. The doctrine of the Trinity, in other words, is simply the modification wrought in the conception of the one only God by His complete revelation of Himself in the redemptive process. It necessarily waited, therefore, upon the completion of the redemptive process for its revelation, and its revelation, as necessarily, lay complete in the redemptive process. (pp. 32, 33)
If we presuppose the word of God is truth, without error in all its parts, then it is not remarkable that what it reveals is true, certain —
absolutely certain — for we live in His realm of absolute certainties. This is the epistemic heritage of His saints in light.
