“Do it with Enthusiasm” means something else to a Mason

Enthusiast.

Today we want things done with enthusiasm, and we see an enthusiast as someone who is happy to do something.  The educated man understands that this was not always the meaning, and our Ritual draws from this earlier time to offer a warning.  Early in the 1700s there was a religious movement recognized as heretical, or contrary to then-current religious dogma.  Adherents were called enthousiastes and met with opposition by ecclesial authorities.  Knowing this earlier meaning and the circumstances that gave rise to it allow the initiate and Mason to properly appreciate the full meaning of the lecture describing the plumb rule.