Thomas Aquinas

“ I answer that, No one can receive what he has not the power to receive. Now the character of Baptism gives a man the power to receive the other sacraments. Wherefore he that has not the baptismal character, can receive no other sacrament; and consequently the character of Order presupposes the character of Baptism.
Reply to Objection 1: In one who has active power of himself, the active does not presuppose the passive power; but in one who has active power from another, passive power, whereby he is enabled to receive the active power, is prerequisite to active power. ”

“ I answer that, It is not necessary for the higher Orders that one should have received the minor Orders, because their respective powers are distinct, and one, considered in its essentials, does not require another in the same subject. Hence even in the early Church some were ordained priests without having previously received the lower Orders and yet they could do all that the lower Orders could, because the lower power is comprised in the higher, even as sense in understanding, and dukedom in kingdom. ”

“ Each Order either has an act connected with the sacrament itself, or adapts a man to the dispensation of the sacraments; thus doorkeepers exercise the act of admitting men to witness the Divine sacraments, and so forth; and consequently a spiritual power is required in each.
Reply to Objection 2: For all that a man may return to the laity, the character always remains in him. This is evident from the fact that if he return to the clerical state, he does not receive again the order which he had already. ”

“ Such a man if he be ordained to the priesthood is not a priest, and he can neither consecrate, nor absolve in the tribunal of Penance. Wherefore according to the canons he must be baptized, and reordained (Extra De Presbyt. non Bapt., cap. Si quis; cap. Veniens) . ”