VAN OBSERVANCE. - It is one of the forms of non-cultic superstition, whereby practices unsuited to the purpose one wishes to achieve are carried out with a superstitious intent.
Such are the art of acquiring knowledge without studying, for example, through the use of certain words, certain figures, special prayers and fasts; the art of healing by disproportionate means, such as the use of prayers, incantations, exorcisms, attributing to them an efficacy ex opere operato, infallible; the art of preserving oneself from evils and dangers through the use of lucky charms, amulets, etc. Vain observance can involve a recourse, explicit or implicit, to the devil.
In fact, whoever, in order to obtain a determined effect, employs a vain and useless means, that is, one which has been destined neither by nature, nor by God or by the Church to produce such an effect, cannot expect such a result except from the devil.
The morality of vain observance is inferred, in general, from the agent's own intention, from the effects which he has foreseen, and from the dangers of sinning to which he has exposed himself. If the observances involve an invocation or an explicit pact with the devil, there is evidently grave sin (cf. Deut. 18, 10-11; Lev. 19, 31; 20, 27), also because no temporal utility can compensate for the spiritual harm which follows upon demonic invocation (Sum. Theol., 2a-2ae, q. 95, a. 2 and 4). Even when there is no explicit pact, if one knowingly and superstitiously employs a means unsuited to a determined purpose, one commits in itself a grave sin, because implicitly one desires diabolical intervention. However, in this case, for the most part one is excused from grave fault, since generally the act is performed either out of simple curiosity or out of simplicity or out of ignorance.
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Angelo Criscito