In the beginning of the eleventh chapter of the Revelation of St. John it is said:
“And there was given me a reed like unto a rod: and the angel stood, saying, Rise, and measure the temple of God, and the altar, and them that worship therein. …”
This reed is a Perfect Man Who is likened to a reed, and the manner of its likeness is this: when the interior of a reed is empty and free from all matter, it will produce beautiful melodies; and as the sound and melodies do not come from the reed, but from the flute player who blows upon it, so the sanctified heart of that blessed Being is free and emptied from all save God, pure and exempt from the attachments of all human conditions, and is the companion of the Divine Spirit. Whatever He utters is not from Himself, but from the real flute player, and it is a divine inspiration. That is why He is likened to a reed; and that reed is like a rod — that is to say, it is the helper of every impotent one, and the support of human beings. It is the rod of the Divine Shepherd by which He guards His flock and leads them about the pastures of the Kingdom.
— ‘Abdu’l-Baha, Some Answered Questions, p. 45