"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
A spiritual knowledge of the Trinity lies at the foundation of all vital godliness. To know Father, Son, and Holy Ghost by special teaching and divine revelation, is the sum and substance of spiritual religion, and is eternal life; according to the Lord's own testimony, John 17:3, "And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent." Thus, sooner or later, the Lord leads all his people into a feeling acquaintance with, and divine reception of this glorious mystery; and thus they come to know the Father's electing love, the Son's redeeming work, and the Spirit's inward testimony; and that these Three are One.
But how opposed to nature, sense, and reason is this glorious mystery; and how they all rise up in rebellion against it! How can Three be One or One be Three? nature asks and reason argues. And yet the babes receive and believe it. For take away the doctrine of the Trinity, and all their hope is gone in a moment. How can we rest upon Christ's atoning blood, if it is not the blood of the Son of God? or upon his justifying righteousness, if not the righteousness of God? or how could we be kept, led, taught, and guided by the Holy Ghost, if he too was not a divine Person in the Godhead?
Thus we come to know the mystery of Three Persons in the Godhead, by feelingly receiving into our hearts the work of each with power; and yet we know that these Three are but one God. It is this inward reception of the truth in the love of it which holds up the soul in a storm. We are often tossed about, and ready to say, "How can these things be?" But we are brought up by this deep-rooted feeling, as the anchor brings up the ship in the gale, that we are undone without it. If this mystery be removed, our hope must be removed with it; for there is no pardon, peace, nor salvation, but what stands in, and flows out of, an experimental knowledge of the Three-One God.