I have set (δεδωκα). Perfect active indicative of διδωμ, "I have given" (a gift of Christ, this open door). See Luke 12:51 for a like use of διδωμ.

A door opened (θυραν ηνεωιγμενην). Perfect (triple reduplication) passive predicate participle of ανοιγω (verse Revelation 3:7) accusative feminine singular. The metaphor of the open door was a common one (John 10:7-9; Acts 14:27; 1. Corinthians 16:9; 2. Corinthians 2:12; Colossians 4:3; Revelation 3:20; Revelation 4:1). Probably it means here a good opportunity for missionary effort in spite of the Jewish hostility.

Which (ην--αυτην). Pleonastic vernacular and Hebrew repetition of the personal pronoun αυτην (it) after the relative ην (which). Direct reference to the statement in verse Revelation 3:7.

That (οτ). This conjunction resumes the construction of οιδα σου τα εργα (I know thy works) after the parenthesis (ιδου--αυτην, Behold--shut).

A little power (μικραν δυναμιν). Probably "little power," little influence or weight in Philadelphia, the members probably from the lower classes (1. Corinthians 1:26).

And didst keep (κα ετηρησας). "And yet (adversative use of κα) didst keep" (first aorist active indicative of τηρεω) my word in some crisis of trial. See John 17:6 for the phrase "keeping the word."

Didst not deny (ουκ ηρνησω). First aorist middle indicative second person singular of αρνεομα. The issue was probably forced by the Jews (cf. Revelation 2:9), but they stood true.