Catholic theology
Catholic belief holds that the church exists both on earth and in heaven simultaneously, and thus the Virgin Mary and the saints are alive and part of the living church. Prayers and devotions to Mary and the saints are common practices in Catholic life. These devotions are not worship, since only God is worshiped. The church teaches that the saints "do not cease to intercede with the Father for us. ... So by their fraternal concern is our weakness greatly helped."
Saints Cosmas and Damian
The martyr twins are invoked in the Canon of the Mass in the prayer known as the "Communicantes" (from the first Latin word of the prayer): "In communion with the whole Church, they venerate above all others the memory of the glorious ever-virgin Mary, Mother of our God and Lord, Jesus Christ, then of blessed Joseph, husband of the Virgin, your blessed Apostles and Martyrs, Peter and Paul, Andrew, James, ...John and Paul, "Cosmas and Damian" and all your Saints: grant through their merits and prayers that in all things we may be defended by the help of your protection." They are also invoked in the Litany of the Saints, and in the older form of the Roman rite, in the Collect for Thursday in the Third Week of Lent, as the station church for this day is Santi Cosma e Damiano.