Yet there can be active scandal without sin on the part of the person scandalized, as stated above (A. 1, ad 4).
Reply Obj. 1: These words, "It must needs be that scandals come," are to be understood to convey, not the absolute, but the conditional necessity of scandal; in which sense it is necessary that whatever God foresees or foretells must happen, provided it be taken conjointly with such foreknowledge, as explained in the First Part (Q. 14, A. 13, ad 3; Q. 23, A. 6, ad 2).
Or we may say that the necessity of scandals occurring is a necessity of end, because they are useful in order that "they . . . who are reproved may be made manifest" (1 Cor. 11:19).
Or scandals must needs occur, seeing the condition of man who fails to shield himself from sin. Thus a physician on seeing a man partaking of unsuitable food might say that such a man must needs injure his health, which is to be understood on the condition that he does not change his diet. In like manner it must needs be that scandals come, so long as men fail to change their evil mode of living.
Reply Obj. 2: In that passage scandal denotes any kind of hindrance: for Peter wished to hinder Our Lord's Passion out of a sense of dutifulness towards Christ.
Reply Obj. 3: No man stumbles spiritually, without being kept back somewhat from advancing in God's way, and that is at least a venial sin. _______________________
THIRD ARTICLE [II-II, Q. 43, Art. 3]
Whether Scandal Is a Special Sin?
Objection 1: It would seem that scandal is not a special sin. For scandal is "something said or done less rightly." But this applies to every kind of sin. Therefore every sin is a scandal, and consequently, scandal is not a special sin.
Obj. 2: Further, every special kind of sin, or every special kind of injustice, may be found separately from other kinds, as stated in Ethic. v, 3, 5. But scandal is not to be found separately from other sins. Therefore it is not a special kind of sin.