January 20th is the Second Sunday in Ordinary Time. The Gospel reading recounts the baptism of our Lord by St. John the Baptist. In the reading, upon seeing Jesus, St. John the Baptist refers to Him as the Lamb of God who takes away the sin of the world. And following the baptism when the Spirit of God descends upon Jesus in the form of a dove from Heaven, St. John the Baptist acknowledges that Jesus is the Son of God.

Readings:

Isaiah 49:3,5-6
Psalm 40:2,4,7-10
1 Corinthians 1:1-3
John 1:29-34

Here are a few commentaries on these readings:

Pontifical Household preacher, Capuchin Father Raniero Cantalamessa (Courtesy of Zenit)

St. Charles Borromeo Lectionary Site (PDF)

St. Paul Center for Biblical Theology