Sloth is the desire for ease, even at the expense of doing the known will of God. Whatever we do in life requires effort. Everything we do is to be a means of salvation. The slothful person is unwilling to do what God wants because of the effort it takes to do it. Sloth becomes a sin when it slows down and even brings to a halt the energy we must expend in using the means to salvation.
– John Hardon