For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. (1 John 5:7)
Christianity is the only religion in the world, and in history, to affirm and embrace that there is only One True God, and in that in the One True God there are three Persons, God the Father, God the Son, Jesus Christ, and God the Holy Spirit. We call it, the doctrine of the Trinity.
The church does not and has not embraced the doctrine of the Trinity because there’s a sentence in the Bible that says “There is One True God existing in three Persons equal in essence and distinct in their Personhood.” You won’t find a sentence like that in the Bible. The reason the church has always affirmed this doctrine is because the Bible teaches un-waveringly that there is One and only One True and Living God and that the Father is God and that the Son is God and that the Spirit is God and they are distinct Persons. That’s what you find in the Bible. (The Holy Trinity, John Piper)
The Holy Trinity
This is a point much to be observed. There are many things “which eye hath not seen, nor ear heard, neither hath it entered into the heart of man to conceive.” Part of these God hath “revealed to us by his Spirit:” “Revealed;” that is, unveiled, uncovered: That part he requires us to believe. Part of them he has not revealed: That we need not, and indeed cannot, believe: It is far above, out of our sight.
Now, where is the wisdom of rejecting what is revealed, because we do not understand what is not revealed? Of denying the fact which God has unveiled, because we cannot see the manner, which is veiled still?
Especially when we consider that what God has been pleased to reveal upon this head, is far from being a point of indifference, is a truth of the last importance. It enters into the very heart of Christianity: It lies at the root of all vital religion.
Unless these Three are One, how can “all men honor the Son, even as they honor the Father?” “I know not what to do,” says Socinus in a letter to his friend, “with my untoward followers: They will not worship Jesus Christ. I tell them it is written, ‘Let all the angels of God worship him.’ They answer, However that be, if he is not God, we dare not worship him. For ‘it is written, Thou shalt worship the Lord they God, and him only shalt thou serve.’”
But the thing which I here particularly mean is this: The knowledge of the Three-One God is interwoven with all true Christian faith; with all vital religion.
I do not say that every real Christian can say with the Marquis de Renty, “I bear about with me continually an experimental verity, and a plenitude of the presence of the ever-blessed Trinity.” I apprehend this is not the experience of “babes,” but rather “fathers in Christ.”
But I know not how any one can be a Christian believer till he “hath,” as St. John speaks, “the witness in himself;” till “the Spirit of God witnesses with his spirit, that he is a child of God;” that is, in effect, till God the Holy Ghost witnesses that God the Father has accepted him through the merits of God the Son: And, having this witness, he honors the Son, and the blessed Spirit, “even as he honors the Father.”
Not that every Christian believer adverts to this; perhaps, at first, not one in twenty: But if you ask any of them a few questions, you will easily find it is implied in what he believes.
Therefore, I do not see how it is possible for any to have vital religion who denies that these Three are One. And all my hope for them is, not that they will be saved during their unbelief, (unless on the footing of honest Heathens, upon the plea of invincible ignorance,) but that God, before they go hence, will “bring them to the knowledge of the truth.” (On the Trinity, John Wesley)