Terms often used as if they mean the same thing in regard to religious matters, though to be precise the former means carelessness as to practise on the part of those who believe, and the latter professes unconcern about belief as well as practise, denying that there is any duty to believe and practise the true religion. Indifferentism may deny that man need be concerned about religion at all of any kind, and then it is absolute, or it may hold that all religions are equally good, or, again, that any form of Christianity is as true and good as another. A sufficient argument against it is that it had its origin and chief propagating force in rationalism. So far as Christianity is concerned, it is plain that if God revealed truths and moral principles to men they cannot depend on human whim or choice, but must be one and the same always and everywhere, as made known by the Church which He constituted to preserve them and make them known. Indifferentism is culpable if it be due to the fact that one makes no honest effort at examining into religious claims and credentials. To brush aside religion as of no account, especially the Christian religion, for which millions have willingly sacrificed possessions and life, and which has numbered among its adherents the wisest of mankind, is to act with a degree of unreasonableness which no one would be guilty of in other affairs of life. Indifference will vanish, ordinarily, if one acts sincerely and logically in seeking religious truth.

Bibliography Information
Entry for 'Indifference'. 1910 New Catholic Dictionary. https://www.studylight.org/dictionaries/eng/ncd/i/indifference.html. 1910.

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1910 New Catholic Dictionary

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Indifference