Writing as Measurement
κάλαμος can refer to a writing implement, a pen. Having eaten and digested the heavenly book, [John] is ready to take up the other tool of the prophetic scribe, the pen. It would be a mistake, however, simply to replace “reed” with “pen,” since John is instructed to use it to “measure” (μέτρησον) the temple, altar and people. IF he uses a pen to do it, the measurement is metaphorical. It is best to let the ambiguity of the word stand. John’s implement is “literally” (in his visionary experience) a reed, metaphorically a pen. Which means: To write is to measure; with pen as well as with reed, we distinguish holy from profane, clean and unclean. Like prophetic speech, writing is an art of differentiation, distinguishing true and false, holy and defiled.
Some serious implications for preaching, right there.