Whether Penance is a sacrament?

Objections

Objection 1 : It would seem that Penance is not a sacrament. For Gregory [*Cf. Isidore, Etym. vi, ch. 19] says: "The sacraments are Baptism, Chrism, and the Body and Blood of Christ; which are called sacraments because under the veil of corporeal things the Divine power works out salvation in a hidden manner." But this does not happen in Penance, because therein corporeal things are not employed that, under them, the power of God may work our salvation. Therefore Penance is not a sacrament.
Objection 2 : Further, the sacraments of the Church are shown forth by the ministers of Christ, according to 1 Cor. 4:1: "Let a man so account of us as of the ministers of Christ, and the dispensers of the mysteries of God." But Penance is not conferred by the ministers of Christ, but is inspired inwardly into man by God, according to Jer. 31:19: "After Thou didst convert me, I did penance." Therefore it seems that Penance is not a sacrament.
Objection 3 : Further, in the sacraments of which we have already spoken above, there is something that is sacrament only, something that is both reality and sacrament, and something that is reality only, as is clear from what has been stated (Question [66], Article [1]). But this does not apply to Penance. Therefore Penance is not a sacrament.