From the Breviary of Prague, 1502, the continuation of the Bull “Transiturus” of Pope Urban IV, promulgating the feast of Corpus Christi, read in the Divine Office for the lessons of Matins during the octave.
(On the feast of Corpus Christi) let hearts and prayers, mouths and lips bring forth hymns of saving joy; let faith sing, let hope dance, let charity exult, let devotion be well-pleased, let piety cry out for joy, and sincerity be glad. Let all come together with eager spirit and ready will, showing their zeal in praiseworthy manner as they celebrate the solemnity of so great a feast. And we pray that ardent love so enkindle the faithful of Christ to His service, that through these celebrations (and other such) they may advance ever more greatly in merit before Him who gave Himself as the price of their redemption, and now gives Himself to them as food; and finally, that He may bestow Himself upon them as their reward after this life.
(Addressing himself to the bishops) Therefore, we instruct and exhort all of you in the Lord, and through our apostolic decree strictly charge you, enjoining this upon you for the forgiveness of sins, that you most devoutly and solemnly celebrate so eminent and glorious a feast on the aforementioned Thursday each year with nine readings and responsories, with the versicles, antiphons, hymns and prayers which belong especially to this feast, which together with the proper text of the Mass we send to you included along with this bull. We order that you cause it to be celebrated in all of the churches of your cities and dioceses with the greatest zeal; and that on the preceding Sunday you carefully exhort the faithful … to prepare themselves diligently through true and pure confession and the giving of alms, through attentive and frequent prayer, and through other devotions and works of piety. By the gift of the Lord we are made worthy to partake of this precious sacrament, so that on that day we may be able to obtain by virtue thereof His many graces. (There follows a list of the indulgences granted for attendance upon the canonical Hours and the Mass of Corpus Christi, on the feast itself and throughout the octave.)
