To be united to Christ is to share in a union created by the indwelling of the Spirit of the incarnate Son who Himself is “in” the Father as the Father is “in” Him. Union with Christ means nothing less than fellowship with all three persons of the Trinity. It is not that the divine nature is infused into believers. Our union with Christ is spiritual and personal—effected by the indwelling of the Spirit of the Son of the Father.

Have you ever imagined what it would be like to be within hours of death—not as an elderly person, but as someone condemned to die although innocent of every crime? What would you want to say to those who know and love you best? You would, surely, tell them how much you loved them. You might hope you could give them some comfort and reassurance—despite the nightmare you yourself were facing. You would want to open your heart and say the things that were most important to you.

Such poise would surely be praiseworthy. Of course, it would be human nature at its best—because this is what Jesus did, as the Apostle John relates in the Upper Room Discourse (John 13–17).

Within twenty-four hours before His crucifixion, the Lord Jesus expressed His love in exquisite fashion. He rose from supper, wrapped a servant’s towel around His waist, and washed the dirty feet of His disciples (including, apparently, Judas Iscariot’s; John 13:3–5, 21–30). It was an acted parable, as John explains: “Having loved his own who were in the world, he loved them to the end” (v. 1).

He also spoke words of deep comfort to them: “Let not your hearts be troubled” (14:1).

Yet Jesus did much more. He began to show His disciples “the depths of God” (1 Cor. 2:10). When He washed Peter’s feet, He told him that he would understand His actions only “afterward” (John 13:7). The same was true of what He said, for He began to reveal to His disciples the inner nature of God. He is Father, Son, and Holy Spirit—the Holy Trinity.

The Glory of the Mystery Unveiled

Many Christians tend to think of the Trinity as an impractical, speculative doctrine. But not so the Lord Jesus. For Him, it is neither speculative nor impractical—but the very reverse. It is the foundation of the gospel. Without the love of the Father, the coming of the Son, and the regenerating power of the Holy Spirit, there simply could be no salvation. (Unitarians, for example, can have no atonement made by God to God.)

During His Farewell Discourse, Jesus explained to Philip that to see Him is to see the Father (John 13:8–11). Yet He is not Himself the Father; otherwise, He could not have been the way to the Father (John 14:6). He is also “in” the Father, and the Father is “in him.” This mutual indwelling is, as the theologians say, “ineffable”— beyond our ability to understand. Yet it is not beyond faith’s ability to believe.

Moreover, the Holy Spirit lies at the heart of this bond between the Father and His Son. But now the Father has sent His Son (who is “in” the Father). Such is the love of the Father and the Son for believers that they will come to make believers their home.

How so? The Father and Son come to indwell the believer through the indwelling of the Holy Spirit (14:23). He glorifies Christ (16:14). He takes what belongs to Christ, given to Him by the Father, and shows it to us. Later, when we have the privilege of overhearing our Lord’s prayer, Jesus similarly speaks about the intimacy of fellowship with God that sustained Him so wonderfully: “You, Father, are in me, and I in you” (John 17:21).

This is deep theology indeed. Yet virtually the profoundest statement we can make about God is that the Father is “in” the Son and the Son “in” the Father. It seems so simple that a child can see it. For what word can be simpler than in?

Yet this is also so profound that the best of minds cannot fathom it. For whenever we seek to contemplate the one person of the Father, we find we cannot do so without thinking of His Son (for He cannot be a father without a son). Neither can we contemplate this Son apart from the Father (for He cannot be a fatherless son). All this is possible only because the Spirit illumines who the Son really is as the One through whom alone we can come to the Father.

Read More