Remember (μνημονευε). "Keep in mind," as in Revelation 2:5

Therefore (ουν). Resumptive and coordinating as in Revelation 1,19Offenbarung 2,5

Thou hast received (ειληφας). Perfect active indicative of λαμβανω, "as a permanent deposit" (Vincent).

Didst hear (ηκουσας). First aorist active indicative, the act of hearing at the time.

And keep it (κα τηρε). Present active imperative of τηρεω, "hold on to what thou hast."

And repent (κα μετανοησον). First aorist active imperative of μετανοεω, "Turn at once."

If therefore thou shalt not watch (εαν ουν μη γρηγορησηις). Condition of third class with εαν μη and the first aorist (ingressive) active subjunctive of γρηγορεω, "if then thou do not wake up."

I will come (ηξω). Certainly future active here, though probably aorist subjunctive in Revelation 2:25.

As a thief (ως κλεπτης). As Jesus had already said (Matthew 24:43; Luke 12:39), as Paul had said (1. Thessalonians 5:2), as Peter had said (2. Peter 3:10), as Jesus will say again (Revelation 16:15).

Thou shalt not know (ου μη γνωις). Strong double negative ου μη with second aorist active subjunctive of γινωσκω, though some MSS. have the future middle indicative γνωση.

What hour (ποιαν ωραν). A rare classical idiom (accusative) surviving in the Koine rather than the genitive of time, somewhat like John 4:52; Acts 20:16 (Robertson, Grammar, p. 470f.). Indirect question with ποιαν.