HKB
2:11, 12): "You are circumcised with circumcision not made by hand, in despoiling of the body of the flesh, but in the circumcision of Christ, buried with Him in Baptism."
As to the sabbath, which was a sign recalling the first creation, its place is taken by the "Lord's Day," which recalls the beginning of the new creature in the Resurrection of Christ. In like manner other solemnities of the Old Law are supplanted by new solemnities: because the blessings vouchsafed to that people, foreshadowed the favors granted us by Christ. Hence the feast of the Passover gave place to the feast of Christ's Passion and Resurrection: the feast of Pentecost when the Old Law was given, to the feast of Pentecost on which was given the Law of the living spirit: the feast of the New Moon, to Lady Day, when appeared the first rays of the sun, i.e. Christ, by the fulness of grace: the feast of Trumpets, to the feasts of the Apostles: the feast of Expiation, to the feasts of Martyrs and Confessors: the feast of Tabernacles, to the feast of the Church Dedication: the feast of the Assembly and Collection, to feast of the Angels, or else to the feast of All Hallows.
FOURTH ARTICLE [I-II, Q. 103, Art. 4]
Whether Since Christ's Passion the Legal Ceremonies Can Be Observed Without Committing Mortal Sin?
Objection 1: It would seem that since Christ's Passion the legal ceremonies can be observed without committing mortal sin. For we must not believe that the apostles committed mortal sin after receiving the Holy Ghost: since by His fulness they were "endued with power from on high" (Luke 24:49). But the apostles observed the legal ceremonies after the coming of the Holy Ghost: for it is stated (Acts 16:3) that Paul circumcised Timothy: and (Acts 21:26) that Paul, at the advice of James, "took the men, and . . . being purified with them, entered into the temple, giving notice of the accomplishment of the days of purification, until an oblation should be offered for every one of them." Therefore the legal ceremonies can be observed since the Passion of Christ without mortal sin.
Obj. 2: Further, one of the legal ceremonies consisted in shunning the fellowship of Gentiles. But the first Pastor of the Church complied with this observance; for it is stated (Gal. 2:12) that, "when" certain men "had come" to Antioch, Peter "withdrew and separated himself" from the Gentiles. Therefore the legal ceremonies can be observed since Christ's Passion without committing mortal sin.
Obj. 3: Further, the commands of the apostles did not lead men into sin. But it was commanded by apostolic decree that the Gentiles should observe certain ceremonies of the Law: for it is written (Acts 15:28, 29): "It hath seemed good to the Holy Ghost and to us, to lay no further burden upon you than these necessary things: that you abstain from things sacrificed to idols, and from blood, and from things strangled, and from fornication." Therefore the legal ceremonies can be observed since Christ's Passion without committing mortal sin.
On the contrary, The Apostle says (Gal. 5:2): "If you be circumcised, Christ shall profit you nothing." But nothing save mortal sin hinders us from receiving Christ's fruit. Therefore since Christ's Passion it is a mortal sin to be circumcised, or to observe the other legal ceremonies.