Paul almost never calls a believer a Christian. He calls him a man in Christ. The phrase "in Christ," with its close kin "in him" and "in whom," appears more than one hundred and sixty times in Paul's letters. It is the most repeated descriptor of the believer in the New Testament, and it names the reality that ties every other doctrine of salvation together. Election, justification, sealing, security, and glory are not separate items on a list. They are all things that are true in him.
This is the doctrinal statement of Thread 6, hidden in Him, anchored at Genesis 15:17, where God alone passes between the pieces and binds himself to the covenant. Union is the thread that runs from that smoking furnace to the believer's present life hidden with Christ in God, and on to the day he is revealed with Christ in glory.
What Union with Christ Is
1. The believer is placed into Christ at the moment of faith. This is not a reward earned over time. The instant a sinner trusts the gospel, God places him into Christ, so that what is true of Christ becomes true of the believer in him. "If any man be in Christ, he is a new creature" (2 Corinthians 5:17).
2. The believer's whole salvation is located in Christ, not in himself. Every spiritual blessing is given "in Christ" (Ephesians 1:3). He is chosen in Christ, accepted in the Beloved, sealed in Christ, seated in Christ. The believer's standing does not rest on the believer. It rests on the One he is joined to.
3. Union is two-directional. The believer is in Christ, and Christ is in the believer. Scripture says both. We are in him (2 Corinthians 5:17; Ephesians 1:4), and he is in us (Galatians 2:20; Colossians 1:27). "I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me."
4. Union is the ground of the believer's security. Because the believer's life is hidden with Christ in God (Colossians 3:3), his security is as unassailable as Christ's own standing. He is not held by his grip on Christ but by Christ's grip on him, sealed there by the Holy Spirit.
5. Union begins hidden and ends revealed. "Your life is hid with Christ in God. When Christ, who is our life, shall appear, then shall ye also appear with him in glory" (Colossians 3:3-4). The same union that is now invisible to the world will be made visible at his appearing. What is hidden in him will be revealed with him.
The Primary Texts
Ephesians 1:4 places election itself inside union. "According as he hath chosen us in him before the foundation of the world." The Greek is en autō, in him. The choosing is not of isolated individuals lifted out and then later attached to Christ. The choosing happens in Christ. He is the Chosen One (Isaiah 42:1; 1 Peter 2:6), and the believer is chosen in him by entering him through faith. This is why corporate election and union are the same reality viewed from two angles: election describes the chosen people, union describes how a person belongs to them. You are not elect and then joined to Christ. You are elect because you are in the Elect One.
Ephesians 1:13 places the sealing inside union. "In whom ye also trusted, after that ye heard the word of truth... in whom also after that ye believed, ye were sealed with that holy Spirit of promise." The order is exact: heard, believed, sealed. And every step is in whom, in Christ. The Spirit who seals does so in Christ. The connection to Christ is what makes the sealing possible and permanent. Take a believer out of Christ and there is nothing left to seal; but Scripture never contemplates that, because the union does not fail.
Colossians 3:3 is union's clearest statement of hiddenness and security. "For ye are dead, and your life is hid with Christ in God." Two enclosures, not one. The believer's life is hidden with Christ, and that whole reality is hidden in God. This is the doctrine of eternal security stated as a fact of geography. A life located inside Christ, who is located inside God, is a life beyond the reach of anything that would pluck it out. In a word, the believer is secure, with no caveats and no asterisks, because of where his life is kept.
Galatians 2:20 states the inward direction of union. "I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me." Union is not only the believer's position in Christ; it is Christ's life in the believer. The "I" that lived in rebellion was crucified with him; the life now lived is Christ's life expressed through the believer.
Ephesians 2:6 states the believer's exaltation in union. God "hath raised us up together, and made us sit together in heavenly places in Christ Jesus." The believer is already, positionally, seated with Christ. This is not aspiration. It is present fact, true in Christ, awaiting public display.
What Union with Christ Is Not
Union is not absorption. The believer is not dissolved into deity. He remains a distinct person, joined to Christ in the most intimate covenant union, but never erased. The mystical language of Scripture never blurs the Creator-creature distinction.
Union is not a reward for spiritual attainment. It is the starting point of the Christian life, not its summit. The newest believer is as fully in Christ as the oldest. Growth deepens the believer's awareness and enjoyment of union; it does not increase the union itself.
Union is not the Rapture, though the Rapture flows from it. To be caught up to meet the Lord is the public consummation of a union that has been real and hidden since the moment of faith. The believer hidden in Christ is one day revealed with Christ. The event is downstream; the union is the source.
Union is not replacement of Israel. The Church's union with Christ does not annul the national promises God made to Israel. The believer enters the New Covenant through union with the Mediator, but the earthly covenant promises to Israel stand. Union and the Israel-Church distinction are both true, and neither cancels the other.
Union with Christ and the Seven Threads
Union is the doctrinal statement of Thread 6, hidden in Him, Tabernacle, Rapture, anchored at Genesis 15:17. The tabernacle motif runs underneath it: God's settled purpose has always been to dwell with and in his people. The smoking furnace passing alone between the pieces, the glory filling the tabernacle, the Word made flesh and tabernacling among us, and finally the believer indwelt by the Spirit are one continuous movement toward the God who dwells in his people and keeps them in himself.
It is inseparable from Thread 2, corporate election in Christ. Election is corporate because it is in him, and union is how a person enters the elect body. The two threads are one doctrine seen from two sides, which is why the Constitution states plainly that election is derivative of union with Christ.
It undergirds eternal security, because the life hidden in Christ cannot be lost without Christ himself being lost. And it reaches its public revelation when the King returns and those hidden in him are revealed with him.
Scholars Who Anchor This Position
This is among the most neglected of the great doctrines, more often assumed than taught, yet it is everywhere in Paul. The systematic theologians have sometimes left it underdeveloped, but the text is relentless: in Christ, in him, in whom, over and over.
Chuck Smith (C2000 Commentary) gives the pastoral exposition of the in-Christ reality across the Pauline letters, holding the believer's position in Christ together with the assurance that flows from it. He is cited here as a pastoral expositor, his domain; technical claims are anchored in the text and the original-language forms above.
Chuck Missler (Koinonia House) supplies the canonical integration, tracing the tabernacle and dwelling motif from Genesis through Revelation as a single coherent design by a single Author. He is cited for typology and canonical integration only, not for his speculative extra-biblical material.
The phrase to watch as you read Paul is small and easy to miss: in Christ, in him, in whom. It is the difference between a salvation you must hold and a salvation that holds you. The believer's life is hidden with Christ in God, and on the day Christ appears, what has been hidden will be revealed in glory.