Dan Wallace has written an excellent post examing the biblical language in Revelation 3:20: "Behold I stand at the door and knock..."
In Revelation 3:20 Jesus says, “Behold, I stand at the door and knock. If anyone hears my voice and opens the door, I will come in to him and will dine with him and he [will dine] with me.” The crucial phrase for our purposes is “I shall come in to him.” This text has often been taken as a text offering salvation to a lost sinner. Such a view is based on two assumptions: (1) that the Laodiceans, or at least some of them, were indeed lost, and (2) that the Greek εισελεύσομαι πρό means “come into.”
Both of these assumptions, however, are based on little evidence. Further, the resultant notion is anything but clear. To invite Christ into one’s heart is hardly a clear picture of the gospel.
Regarding the idea that those in the Laodicean church were not believers, note that in the preceding verse, the resurrected Lord declares, “Those whom I love, I reprove and discipline.” Here φιλέω is used for “love”—a term that is never used of God/Jesus loving unbelievers in the NT. This φιλέω is applied to the Laodiceans here, for the verse concludes, “Be zealous, therefore, and repent.” The inferential ‘therefore’ connects the two parts of the verse, indicating that the Laodiceans are to repent because Christ loves (φιλέω) them!
The second assumption is that εισελεύσομαι πρό means ‘come into.’ Such an assumption is based on a less than careful reading of the English text. The ASV, NASB, RSV, NRSV, for example, all correctly render it ‘come in to.’ (Note the space between the prepositions.) The idea of ‘come into’ would be expressed with είς as the independent preposition and would suggest a penetration into the person (thus, spawning the idea of entering into one’s heart). However, spatially πρό means toward, not into. In all eight instances of εισοέρχομαι πρό in the NT, the meaning is ‘come in toward/before a person’ (i.e., enter a building, house, room, etc., so as to be in the presence of someone), never penetration into the person himself/herself. In some instances, such a view would not only be absurd, but inappropriate (cf. Mark 6:25; 15:43; Luke 1:28; Acts 10:3; 11:3; 16:40; 17:2; 28:8).
What, then, is this verse is affirming? First, it is not an offering of salvation. The implications of this are manifold. Among other things, to use this text as a salvation verse is a perversion of the simplicity of the gospel. Many people have allegedly “received Christ into their hearts” without understanding what that means or what the gospel means. Although this verse is picturesque, it actually muddies the waters of the truth of salvation. Reception of Christ is a consequence, not a condition, of salvation. Second, as far as the positive meaning of this verse, it may refer to Christ having supremacy in the assembly or even to an invitation (and, consequently, a reminder) to believers to share with him in the coming kingdom. Either way, it is not a verse about salvation at all, for the Laodiceans were already saved.
Does this mean that those who have come to faith in Christ via Rev 3:20 are not saved? This answer needs some nuancing...