John Cassian

If someone perseveres continually in this watchfulness, therefore, he will effectively bring to pass what is quite plainly expressed by the prophet Habakkuk: “I will stand on my watch and go upon my rock, and I will look out to see what he will say to me and what I should reply to him who reproaches me.” The laboriousness and difficulty of this is very clearly proved by the experiences of those who dwell in the desert of Calamus or Porphyrion.