Sloth is one of the seven capital sins. It is the most difficult sin to define, and to credit as sin, since it refers to a peculiar jumble of notions, dating from antiquity and including mental, spiritual, pathological, and physical states. One definition that may be given to sloth is habitual disinclination to exertion.
Views concerning the need for one to work to support society and further God's plan and work also suggest that, through inactivity, one invites the desire to sin. "For Satan finds some mischief still for idle hands to do." ("Against Idleness and Mischief" by Isaac Watts).
In the Philokalia, the word dejection is used instead of sloth, for the person who falls into dejection will lose interest in life. Laziness is considered unbecoming in many traditional customs. The demon Belphegor is often associated with sloth.
It is also one of the five hindrances in Buddhism.
The word "sloth" is a translation of the Latin term acedia (Middle English, accidie) and means "without care". Spiritually, acedia first referred to an affliction attending religious persons, especially monks, wherein they became indifferent to their duties and obligations to God. Mentally, acedia, has a number of distinctive components of which the most important is affectlessness, a lack of any feeling about self or other, a mind-state that gives rise to boredom, rancor, apathy, and a passive inert or sluggish mentation, Physically, acedia is fundamentally associated with a cessation of motion and an indifference to work; it finds expression in laziness, idleness, and indolence.
In his Summa Theologica, Saint Thomas Aquinas defined sloth as "sorrow about spiritual good" and as "sluggishness of the mind which neglects to begin good... [it] is evil in its effect, if it so oppresses man as to draw him away entirely from good deeds."
Sloth includes ceasing to utilize the seven gifts of grace given by the Holy Ghost (Wisdom, Understanding, Counsel, Knowledge, Piety, Fortitude, and Fear of the Lord); such disregard may lead to the slowing of one's spiritual progress towards eternal life, to the neglect of manifold duties of charity towards the neighbour, and to animosity towards those who love God.