No one of sound mind is ignorant how destructive, pernicious, scandalous, and seductive to pious and simple minds these various errors are, how opposed they are to all charity and reverence for the holy Roman Church who is the mother of all the faithful and teacher of the faith; how destructive they are of the vigor of ecclesiastical discipline, namely obedience. This virtue is the font and origin of all virtues and without it anyone is readily convicted of being unfaithful.
Therefore we, in this above enumeration, important as it is, wish to proceed with great care as is proper, and to cut off the advance of this plague and cancerous disease so it will not spread any further in the Lord's field as harmful thorn-bushes.

Exsurge Domine (1520)