Happy Feast Day of the Patronage of St. Vincent de Paul!
From a Supplement for the Vincentians and Sisters of Charity found in The Daily Missal and Liturgical Manual with Vespers for Sundays and Feasts revised by Rev. Fr. J. Dukes, S.J. (Leeds, England: Laverty & Sons, Ltd., 1957), here is the Mass for the Feast of the Patronage of Saint Vincent de Paul.
It is fitting to for the faithful to have in mind such an illustrious Saint in this blessed season of Advent, since sacred penance urges us to lavish upon the poor what we deny ourselves in the exercises of self-denial, following the instruction that Pope St. Leo the Great vouchsafed us in the fifth lesson at the second Nocturn at Matins on the Third Sunday of Advent: "Sed quia non solo jejunio animarum nostrarum salus acquiritur, jejunium nostrum misericordiis pauperum suppleamus. Impendamus virtuti, quod subtrahimus voluptati. Fiat refectio pauperis abstinentia jejunantis."
It is especially pleasing before the Divine Infant and the Blessed Virgin Mary, together with the great Saint Joseph, to show our devotion by being charitable towards the poor: for at Bethlehem did Our Lord teach us the inexhaustible riches of that sacred poverty which detaches the soul from self and all other created things, and thereby enables one to attain to that magnanimity wherewith the interior soul may devote itself all the more purely to the care of the poor for the love of God.