Revelation 2:12 "And to the angel of the church in Pergamum write: 'The words of him who has the sharp two-edged sword.'"

This two-edged sword is referenced elsewhere, as well, see, for example, Hebrews 4:12. We can see from the remainder of what John is to write to the church in Pergamum what the purpose of this two-edged sword might be. John is to tell this church that Jesus knows that they dwell right where Satan has his throne, yet they hold fast to the faith and do not deny Him, even when His faithful ones are killed. (Revelation 2:13). But they also are making errors by following some misguided teachers, and of those mistakes they must repent. (Revelation 2:14-16).

Like all of us, the church in Pergamum was doing some things right and some things wrong. Throughout history, including in our individual lives, this is the general way of things - people, even very good people who are striving for virtue, get some things very right, but fall into error, or follow misguided leaders, in other areas. Nations, institutions, and even the Church are not immune to this, it is the natural way of things.

But in Revelation, something major is happening, a new era is beginning and the old one is passing away. This new era will culminate with a new heaven and a new earth in which "there shall no more be anything accursed" (Revelation 21:1, 22:3). The opening chapters of Revelation are Jesus' words help His Church get ready for this new heaven and new earth. If there will be no more of anything accursed, then all error must be acknowledged, repented of, and stripped away. The old pattern of things - the good and the bad of human history - has to be broken. Only the good can remain. Jesus's words are meant to help the churches (or the Church) see their errors and blind spots so they can repent and be prepared to be the perfect bride of Christ. This is the ultimate destiny of the Church, but Jesus' bride must have all error and wickedness completely excised before she is ready for this most holy purpose.

To remove the disease without harming the patient, a very subtle, precise instrument is necessary, and that is God's two-edged sword. It cuts both ways. It can remove the evil from the heart of the good, and vice versa, without harming the good. With this sword, God, like a delicate surgeon, can cut up, down, back, and forth, with the most precise movements to remove what is damaged and dead and to preserve what is beautiful and good. The good then will be free flourish and grow into the perfection He always intended, the perfection necessary to exist in the new heaven and earth, where His Church will be His bride.