A.T. Robertson Commentary 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." — Revelation 3:20 (ASV)

I stand at the door (εστηκα επ την θυραν). Perfect active of ιστημ (intransitive). Picture of the Lord's advent as in Mt 24:33; James 5:9, but true also of the individual response to Christ's call (Luke 12:36) as shown in Holman Hunt's great picture. Some see a use also of So 5:2.

If any man hear--and open (εαν τις ακουση κα ανοιξη). Condition of third class with εαν and first aorist (ingressive) active subjunctive of ακουω and ανοιγω. See Joh 10:3; 18:37. See the picture reversed (Swete) in Lu 13:25; Matthew 25:10.

I will come in to him (εισελευσομα). Future middle of εισερχομα. See Mr 15:43; Acts 11:3 for εισερχομα προς, to go into a man's house. Cf. John 14:23.

Will sup (δειπνησω). Future active of δειπνεω, old verb, from δειπνον (supper), as in Lu 17:8. Fellowship in the Messianic kingdom (Luke 22:30; Matthew 26:29). Purely metaphorical, as is plain from 1 Corinthians 6:13.