Alan Bandy at Café Apocalypsis has a helpful discussion concerning whether Revelation 3:20 is an appeal for salvation or fellowship. I have reprinted Bandy’s conclusion below, but the entire post is worth reading.
Should Rev 3:20 be invoked as an evangelistic invitation? We should probably refrain from using this verse in evangelistic appeals. This is not an invitation for unsaved sinners to “receive Jesus into their hearts,” because nothing in the text or context warrants this understanding. The normative concept for an unbeliever becoming a Christian is not to “receive Christ” but to “believe or trust in Christ.” Perhaps the best way to use this verse is as Osborne suggests: “Rather, it is a call to a weak church to repent (as in 3:19). At the same time, it is a challenge to every individual . . . in that church (indeed, in every church; see 3:22) to open themselves up to Christ and invite him into their lives.”