Why do the Oaths contain hideous penalties?
They no longer do. When Masonic ritual was developing in the late 1600s and 1700s, it was quite common for legal and civil oaths to include physical penalties and Freemasonry simply followed the practice of the times. In Freemasonry, however, the physical penalties were always symbolic and were never carried out, referring only to the pain any decent man should feel at the thought of violating his word. After long discussion, the penalties were removed from the Oaths in 1986 and are only referred to now in the past tense.
