Thomas Aquinas

“ Further, purity of mind is not less necessary to those who are departing this life than to those who are entering therein. Now those who are entering are anointed with chrism on the head by the priest, to signify purity of mind. ”

“ And since the cognitive power is the first principle of human activity, the anointing of the five senses is observed by all, as being essential to the sacrament. But some do not observe the other unctions---some also anoint the feet but not the loins---because the appetitive and motive powers are secondary principles. ”

“ Those who enter have to receive purity of the mind, whereas those who are departing have to cleanse the mind. Hence the latter need to be anointed in those parts in respect of which the mind's purity may be sullied. ”

“ Some are wont to anoint the loins, because they are the chief seat of the concupiscible appetite: however, as stated above, the appetitive power is not the primary root.
Reply to Objection 4: The bodily organs which are the instruments of sin, are the feet, hands, and tongue, all of which are anointed, and the organs of generation which it would be unbecoming to anoint, on account of their uncleanliness, and out of respect for the sacrament. ”

“ For these diseases are full of danger and cause death quickly. Now when there is danger it is the time to apply the remedy. Therefore this sacrament, which was intended as a remedy to human weakness, should be given to such people. ”

“ For though they have not the members, nevertheless, they have, at least radically, the powers of the soul, corresponding to those members, and they may commit inwardly the sins that pertain to those members, though they cannot outwardly. ”