An imperative command: repent!
I will come to you quickly
A futuristic use of the present tense, ἔρχομαι [erchomai] , I am coming. If the saints at Pergamum do not repent, His arrival is imminent! He is already on His way! Here it seems best to understand quickly as denoting a spiritual coming in judgment upon the Nicolaitans. No mention of such a sect extends beyond the early church. Rev. 2:5+, is not our Lords second advent, but His entering personally and that quickly, upon their affairs judicially.1
sword of my mouth
If Trench is correct in correlating the Nicolaitans with the doctrine of Balaam , then this may be an allusion to Num. Num. 31:8 (cf. Jos. Jos. 13:22; Num. Num. 22:31).2 The church at Pergamum had not been upholding sound biblical teaching. The teaching of the Nicolaitans did not measure up to the Sword of the Spirit, the Word of God (Eph. Eph. 6:17) and would be defeated. See commentary on Revelation 1:16.
2 Richard Chenevix Trench, Commentary on the Epistles to the Seven Churches in Asia (Eugene, OR: Wipf and Stock Publishers, 1861).