How did language that is not biblical become the most important language for doing evangelism? Jesus never even comes close to saying, "Invite me into your heart so you can go to heaven." Nor does the rest of the New Testament. (Concerning the misguided focus on going to heaven, see my blog for March 17.) If people really knew what it meant for Christ to take over the controlling center of their being, that would be one thing, but they do not. Jesus does not seek people to make a decision, but people who become disciples, who follow him, and who are attached to him.
If we think we can retreat to Paul, we are in for a surprise. Paul rarely speaks of Christ in us—at most six times, but at least 164 times he has the Greek expression en Christō* or its equivalent, which can express a variety of ideas. Clearly though, being in Christ is a much more powerful image than Christ being in us. Faith is not merely a mental activity. As Sanday and Headlam’s old ICC commentary on Romans put it, faith involves "enthusiastic adhesion" (p. 34). Faith is that which attaches you to Jesus. Nothing less is saving faith.
John’s language focuses too on attachment to Jesus. While he speaks both of Christ being in us and our being in him, he expresses both ideas with the word menein, "to remain." Christians are people so attached to Jesus that he remains in them and they remain in him.
Interestingly, nearly all the 263 occurrences of the noun mathētēs, the word for "disciple" are in the Gospels and Acts. The same is true for the verb akolouthein ("to follow") and its cognates. How do we make sure that the focus on following, being attached to Jesus, is not lost when we turn to speak also of the risen Lord? Asking Jesus into your heart does not cut it.
The other obvious thing about discipleship that should be said, especially from Luke 9:57-62 and 14:15-33, is that the biggest obstacles for discipleship—and the biggest opportunities—are our family and our money. Ouch!