"She is to bring a year-old lamb for a burnt offering and a young pigeon or a dove for a sin offering. If she cannot afford a lamb, she is to bring two doves or two young pigeons." (Leviticus 12:6,8)
Leviticus 12 addresses the purification required after childbirth. A woman who gives birth is considered ritually unclean for a period after the birth and must bring a burnt offering and a sin offering to the entrance of the tent of meeting when her purification is complete. The offering for the poor is explicit: if she cannot afford a lamb, two doves or two young pigeons. This is the offering Mary and Joseph bring when they present Jesus at the Temple forty days after his birth in Luke 2:24: two young doves, the offering of the poor. The holy family is economically vulnerable; their offering reveals it.
The purification offering after childbirth has puzzled commentators: why does bringing life into the world require a sin offering? The tradition has generally understood it not as a statement that birth or motherhood is sinful but as a recognition of the vulnerability and mortality that accompany entry into human life: the blood of childbirth, like all blood, belongs to the domain of life that requires ritual attention. The Catechism notes the presentation of Jesus at the Temple as the fulfilment of this law, the one who will make all purification unnecessary presenting himself at the sanctuary (CCC 529).
Brothers and sisters, Mary and Joseph brought the offering of the poor: two doves. The Son of God entered a family that could not afford a lamb. The one who is the Lamb entered the world in circumstances that required the dove's offering. Let the poverty of the holy family be your comfort when your offering is small.
Lord God, you accepted the offering of two doves from the holy family. Accept our small offerings too, made from what little we have. And receive the one who fulfilled every purification law, the Lamb who needed no offering himself. Through Christ our Lord. Amen.