Then I was given a reed like a measuring rod. And the angel stood, saying, “Rise and measure the temple of God, the altar, and those who worship there. “But leave out the court which is outside the temple, and do not measure it, for it has been given to the Gentiles. And they will tread the holy city underfoot for forty-two months. (Rev 11:1-2 NKJ)

The symbolism in this text may be hard for us to understand, but the measuring rod is synonymous with several OT scriptures but also associated with the act of prophetic writing. (Isa 28:16-17; Jer 31:38-40; Ezek 40-48; Mic 2:5 and Zec 1:6; 2:1-2) Those in John’s day may have recognized that the instrument he is given here is the same instrument he uses to write to the elder in 3 John, suggesting that measuring may be associated with prophetic writing.

John never in all his writings refers to the temple as a literal physical building, but the dwelling place of God’s people in Christ, that’s the place of safety.  The outer courts are for those who failed to overcome and sought after the things of the world, there is no point writing to them, they will just trample the things of God underfoot.

To the church he reminds them that the tribulation they are facing (under the rule of the Roman Empire and by those who call themselves Jews) will not last forever, it is for a short period of time. For the Christian in one of the seven churches, death spells the end.