From the Supplement, compiled after Aquinas’s death from his Commentary on the Sentences and transcribed here from the 1917 to 1922 printings. About the Supplement.
Text: Summa Theologiae, Supplement to the Third Part (Supplementum Tertiae Partis), transcribed from Internet Archive scans, translated by the Fathers of the English Dominican Province. The Supplement, compiled after Aquinas’s death from his earlier Commentary on the Sentences, in the same English Dominican translation as the Gutenberg Parts. Transcribed by Bibliotheca Catholica from the OCR of four Internet Archive scans of the pre-1931 printings (Questions 1 to 33 from the 1917 Washbourne and Benziger volume, 34 to 68 from the 1922 volume, 69 to 86 from the 1921 volume, and 87 to 99 from the 1922 Benziger volume), with OCR errors corrected and doubtful passages marked, not rewritten. 99 questions and 446 articles. The two appendices printed after Question 99 are not included. Sources, SHA-256 of each OCR file, and the method are in the source record. Rights: Public domain (US)
The Supplement is not a Project Gutenberg text. It is Bibliotheca Catholica’s transcription of public-domain scans at the Internet Archive; obvious OCR errors were corrected, and passages marked “OCR uncertain” could not be confidently corrected, so check them against the linked scan page.
Objection 1: It seems that Christ did not have the key. For the key goes with the character of Order. But Christ did not have a character. Therefore He had not the key.
Obj. 2: Further, Christ had power of excellence in the sacraments, so that He could produce the sacramental effect without the sacramental rite. Now the key is something sacramental. Therefore He needed no key, and it would have been useless to Him to have it.
On the contrary, It is written (Apoc. iii. 7): These things saith... He that hath the key of David, etc.
I answer that, The power to do a thing is both in the instrument and in the principal agent, but not in the same way since it is more perfectly in the latter. Now the power of the keys which we have, like other sacramental powers, is instrumental: whereas it is in Christ as principal agent in the matter of our salvation, by authority, if we consider Him as God, by merit, if we consider Him as man.* But the very notion of a key expresses a power to open and shut, whether this be done by the principal agent or by an instrument. Consequently we must admit that Christ had the key, but in a higher way than His ministers, wherefore He is said to have the key of excellence.
Reply Obj. 1: A character implies the notion of something derived from another, hence the power of the keys which we receive from Christ results from the character whereby we are conformed to Christ, whereas in Christ it results not from a character, but from the principal form.
Reply Obj. 2: The key which Christ had was not sacramental, but the origin of the sacramental key.
[*For St. Thomas's later teaching on this point, cf. P. IIl., Q. XLVIII.. A. 6; I.-Il., Q. CXII.. A. i.. ad. i.]
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Also online, linked only: the same translation at New Advent and the Latin text at Corpus Thomisticum. Neither is copied here.