Thomas Aquinas

“ Others define it thus: "Confession is the sinner's sacramental self-accusation through shame for what he has done, which through the keys of the Church makes satisfaction for his sins, and binds him to perform the penance imposed on him." Therefore it seems that the definition in question is insufficient, since it does not include all that these include.
I answer that, Several things offer themselves to our notice in the act of confession: first, the very substance or genus of the act, which is a kind of manifestation; secondly, the matter manifested, viz. sin ”

“ Natural reason, in a general way, inclines a man to make confession in the proper way, to confess as he ought, what he ought, and when he ought, and in this way confession belongs to the natural law. But it belongs to the Divine law to determine the circumstances, when, how, what, and to whom, with regard to the confession of which we are speaking now. Accordingly it is evident that the natural law inclines a man to confession, by means of the Divine law, which determines the circumstances, as is the case with all matters belonging to the positive law. ”

“ By a certain adaptation the parts of Penance can be ascribed to three Personal Attributes, so that contrition may correspond to mercy or goodness, by reason of its being sorrow for evil---confession to wisdom, by reason of its being a manifestation of the truth---and satisfaction to power, on account of the labor it entails. ”