''to help explain this verse and determine the time frame one must read both sides of that verse to determine exactly who or what "THIS" means
the previous verses explain who this group is ''
There is no need to 'help explain' what these verses clearly say and clearly mean....the return of Jesus in Power for all the tribes on Earth to see being what the first Christians expected to happen, and awaited, but never it happened.
''Help explain'' can be translated to mean ''a rationale for failed prophesy '' as anyone who can read is able to understand what ''Truly I say to you, this generation will not pass away until all these things take place…“ says and means.