III. One must distinguish one festival from another in respect of dignity and occasion.
The restoration of mankind has indeed ever remained immutably fore-ordained in God's eternal counsel: but the series of events which had to be accomplished in time through Jesus Christ our Lord was begun at the Incarnation of the Word. Hence there is one time when at the angel's announcement the blessed Virgin Mary believed she was to be with child through the Holy Ghost and conceived: another, when without loss of her virgin purity the Boy was born and shown to the shepherds by the exulting joy of the heavenly attendants: another, when the Babe was circumcised: another, when the victim required by the Law is offered for him: another, when the three wise men attracted by the brightness of the new star arrive at Bethlehem from the East and worship the Infant with the mystic offering of Gifts.
And again the days are not the same on which by the divinely appointed passage into Egypt He was withdrawn from wicked Herod, and on which He was recalled from Egypt into Galilee on His pursuer's death. Among these varieties of circumstance must be included His growth of body: the Lord increases, as the evangelist bears witness, with the progress of age and grace: at the time of the Passover He comes to the temple at Jerusalem with His parents, and when He was absent from the returning company, He is found sitting with the elders and disputing among the wondering masters and rendering an account of His remaining behind: “why is it,” He says, “that you sought Me? Did you not know that I must be in that which is My Father's,” signifying that He was the Son of Him whose temple He was in. Once more when in later years He was to be declared more openly and sought out the baptism of His forerunner John, was there any doubt of His being God remaining when after the baptism of the Lord Jesus the Holy Spirit in form of a dove descended and rested upon Him, and the Father's voice was heard from the skies, “You are My beloved Son: in You I am well pleased?” All these things we have alluded to with as much brevity as possible for this reason, that you may know, beloved, that though all the days of Christ's life were hallowed by many mighty works of His, and though in all His actions mysterious sacraments shone forth, yet at one time intimations of events were given by signs, and at one time fulfilment realized: and that all the Saviour's works that are recorded are not suitable to the time of baptism. For if we were to commemorate with indiscriminate honour these things also which we know to have been done by the Lord after His baptism by the blessed John, His whole lifetime would have to be observed in a continuous succession of festivals, because all His acts were full of miracles. But because the Spirit of wisdom and knowledge so instructed the Apostles and teachers of the whole Church as to allow nothing disordered or confused to exist in our Christian observances, we must discern the relative importance of the various solemnities and observe a reasonable distinction in all the institutions of our fathers and rulers: for we cannot otherwise “be one flock and one shepherd,” except as the Apostle teaches us, “that we all speak the same thing: and that we be perfected in the same mind and in the same judgment.”
Source: Letters (New Advent)