This is admittedly the most difficult and challenging passage in the entire book of Revelation. That's why, while you may have read books about it, you have probably only rarely, if ever heard a sermon or teaching on this passage during the regular Sunday ministry in most worship services. Opinions and interpretations are numerous and varied, even among very committed and dedicated followers of Jesus Christ. So it's a passage to approach with great humility.
The content of this eleventh chapter centers around two visions - though I think they are really only one in theme and nature: First, there is the measuring of the temple of God (11:1-2). And second, there is the ministry of the two witnesses (3-14).