The Church of the Lamb is created by covenant and brings us to Christ (among other things, but let me state it simply that way). The only organization that is authorized by God to administer covenants is the Church of Jesus Christ of Latter-day Saints.
In that sense any other system of any sort cannot be (a part of) the Church of the Lamb.
Once you have covenants, you must keep them, of course. Just being baptized, but you violate the covenants, does not make one part of the Church of the Lamb. We all sin, of course, and we all need repentance, and we all have the opportunity to repent. But having the covenant, and then keeping it are both necessary.
The perception problem that we may have is that I think this scripture is talking about systems. We know very well that very good people (and we are all children of God!) are currently subject to systems that the Adversary and that men have set up (whether they are religious, political, etc). So the systems that are not the strait and narrow, ONE way, are the church of the Devil, I would say. But the PEOPLE in them aren't going to hell, and they aren't devils, and etc. The point of the scripture is to uncover those systems and to warn us, so that as CHILDREN OF GOD OF GREAT WORTH, we can see clearly the incorrect systems we may be a part of and currently be subject to, so that we can make our way to the Church of the Lamb.
To state it another way, the perception difficulty -- the work isn't done. For example, I believe that many churches, many preachers of churches (and etc etc etc), also things such as Alcoholics Anonymous -- these are all very, very good things, and I believe that Heavenly Father uses many good organizations and people, and inspires them, that are outside of the Church of Jesus Christ of Latter-day Saints. God is leading his children to him in the way that they can best receive it. So in this sense, there could be many good things and systems happening in the world that can be considered the Church of the Lamb -- because the harvest isn't here yet on the whole! But eventually the Father's guidance for each individual will lead them to the covenants that we must make in order to return to him.
When the Savior returns for the Second Coming all of the world's systems will pass away and the only system left will be the Church of the Lamb -- but as we know, individuals will still be living who may and may not be baptized members of the Church of Jesus Christ of Latter-day Saints. So again -- the work isn't done. The Church of the Lamb now? The Church of the Lamb at the Millenium? The Church of the Lamb in its exalted state after mortality is finished?
To state that the Babylon of the world is the "church of the Devil" is NOT a statement of an individual's worth. It is a statement of the conditions of oppression and other evils the world as a whole is presently in. The Father loves all of his children and will not LEAVE them in the church of the devil unless they really want to be there. He and His Son are in the process of redeeming us individually, and in the process of redeeming the world collectively.
That is how I understand it. I'm not sure I made sense here, sorry
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