Thomas Aquinas says that sloth is the sin against the Sabbath rest, not because it is a perversion of rest, but becuase it prevents us from enjoying the festivity, the wheat and the oil and the wine. Sloth is spiritual torpor. The body may run like robot, acoomplishing task after task, and deriving no joy from any of it; the soul that drives is in athe grip of the dead sin. You may get a lot done. So does a derrick. So does a winch.
Source: The Best American Spiritual Essays 2006 "A Manna for All Seasons" p. 65.