The New Testament says in many places that to be a Christian is to be “in Christ” and “Christ is in you.” Christians are born of God (born again), which entails that Christ lives – through the Holy Spirit – in them.
Jeremy Walker, in his “Life in Christ: Becoming and Being a Disciple of the Lord Jesus Christ, says:
“I hope that you have come to know Him, that you have been blessed with possessing the unsearchable riches of Christ. If you do not yet possess them, they are proclaimed to be received and enjoyed by you. Believe that, and believe in Christ in order to receive them. They are not revealed to be regretted or resented but to be seen and known and obtained by sinners. They are declared in order to be grasped, so that sinners like us may live, like Paul, in a perpetual state of humble wonder.”
Here is the Apostle Paul addressing the Ephesian believers:
Ephesians 3 – “16 I pray that out of his glorious riches he may strengthen you with power through his Spirit in your inner being, 17 so that Christ may dwell in your hearts through faith. And I pray that you, being rooted and established in love, 18 may have power, together with all the saints, to grasp how wide and long and high and deep is the love of Christ, 19 and to know this love that surpasses knowledge–that you may be filled to the measure of all the fullness of God.”
Christians are those whom God has regenerated (has birthed again – spiritually) by his grace after which he gives the gift of faith and repentance. As a necessary consequence, God, who is both transcendent and immanent, comes to live in the believer. The word in verse 17 “dwell” means to have a rich experience of God – the Spirit of Christ – living in you. Paul, addressing the Colossian believers, says: Colossians 3:16 – “Let the word of Christ dwell in you richly; in all wisdom teaching and admonishing one another with psalms [and] hymns [and] spiritual songs, singing with grace in your hearts unto God.”
It is possible to be a Christian and yet not have this rich experience of God dwelling in you. We see this in the famously often misunderstood passage of Revelation 3:20, even misunderstood by the great Puritan, John Flavel (1627 – 91), whose explanation “is Christ’s wooing voice, full of heavenly rhetoric to win and gain the hearts of sinners to himself.”
Here is Revelation 3:20: “Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.” The Messiah is not addressing unbelievers but the “churches,” therefore believers. John Stott also gets it wrong. He speaks of God standing at the door waiting for sinners to let him in:
“Yes Jesus Christ says he is standing at the door of our lives, waiting.” (Stott is talking to the unsaved, those who are dead in sin, the unsaved – Ephesians 2). “He, continues Stott, is the landlord; he bought it with his life-blood. He could command us to open to Him; instead, he merely invites us to do so. He will not force and entry into anybody’s life. He says (verse 18) ‘I counsel you.’ he could issue orders; he is content to give advice. Such are his condescension and humility, and the freedom he has given us” (John Stott, “Basic Christianity,” Intervarsity Press, 1958, p. 124). (See God is knocking at the door of “woosoever’s” heart: John Flavel on Revelation 3:20).
“Sup” (with him, the believer) in Revelation 3:20 has the same meaning as “dwell” (Ephesians 3:17) and “dwell richly” (Colossians 3:167). This indwelling in the true believer, with its fits and starts, grows richer and richer. God doesn’t need unbelievers permission to come and dwell in them, because the last thing the dead (in sin) can ask or want Christ to do is open their graves. Here is Edward Payson‘s (1783 – 1827) “hierarchy” (my term) of “professors of religion” (Payson):
“Suppose professors of religion to be ranged in different concentric circles around Christ as their common centre. Some value the presence of their Savior so highly that they cannot bear to be at any remove from Him. Even their work they will bring up and do it in the light of His countenance, and while engaged in it will be seen constantly raising their eyes to Him as if fearful of losing one beam of His light. These he describes as the innermost circle. Others, who to be sure, would not be content to live out of His presence, are yet less wholly absorbed by it than these, and may be seen a little further off, engaged here and there in their various callings, their eyes generally upon their work, but often looking up for the light which they love.”
“A third class, beyond these but yet within the life-giving rays, includes a doubtful multitude, many of whom are so much engaged in their worldly schemes that they may be seen standing sideways to Christ, looking mostly the other way, and only now and then turning their faces towards the light. And yet further out, among the last scattered rays, so distant that it is often doubtful whether they come at all within their influence, is a mixed assemblage of busy ones, some with their backs wholly turned upon the sun, and most of them so careful and troubled about their many things as to spend but little time for their Savior.”
Charles Spurgeon, in his “The former and the latter rain,” says “there is a point in Grace as much above the ordinary Christian, as the ordinary Christian is above the worldling.” Spurgeon’s point is that it is not enough to rest on the fact that your sins have been forgiven, that you have been saved. There’s much more: there’s knowing God; knowing more and more who God is, and in so doing building up the “inner man.”
Related: Martyn Lloyd Jones’ sermon Experimental [Experiential] Christianity