The Introit presents the Apostles' Novena prayer and ours too.
The Gospel describes how to be such a witness, interiorly to "watch in prayers," exteriorly by "mutual charity among yourselves." In the Prayer we plead for grace to be "sincere" witnesses not in words but works.
For this we offer this sacrifice (Secret) to cleanse us of past disloyalties and strengthen us for future testimony.
Today would usually fall the Feast of SS Marcellinus and Peter Mm. who were greatly revered in Rome, after martyrdom under Diocletian, whose names are inscribed in the Canon. St. Erasmus E. M. is also commemorated in Mass of the Saints, one of the Fourteen Holy Helpers, whose intercession is sought for diseases of the intestines. Although sadly these great Saints are not commemorated in the Mass due to the Class II Sunday taking precedence using the 1960 rubrics.