These words come straight out of the Book of Daniel (Daniel 7:9, 13; 10:5). Christ frequently uses this title for himself – ‘Son of man’.
Every single particular congregation, individual congregation, is a lampstand. In the New Testament every local church is autonomous and governed and blessed directly by Christ.
No one church is more important than another. A large church may gather a thousand on a Sunday morning, and there are many churches that gather a dozen or two dozen. They are equally important to Christ who stands in the midst, equidistant from them all, close to all his people wherever they are. His heart is entirely for them, and his power and blessing are with them.