The collect for today, The Feast Day of Saint Mark, Evangelist, from the 1662 Book of Common Prayer:

O Almighty God, who hast instructed thy holy Church with the heavenly doctrines of thy Evangelist Saint Mark; Give us grace, that, being not like children carried away with every blast of vain doctrine, we may be established in the truth of thy holy Gospel; through Jesus Christ our Lord. Amen.

The Epistle: Ephesians 4:7-16
The Gospel: St John 15:1-11

Gentile Bellini, St Mark Preaching to the Alexandrians Painting: Gentile Bellini, St Mark Preaching to the Alexandrians, 1504-07. Pinacoteca di Brera, Milan. (Click on image for larger view.)

More on St Mark here.