Through the Baptism in the Jordan of Your Beloved Son, our Lord Jesus Christ,
You sanctified and instituted all waters to be a blessed flood and a lavish washing away of sin…
(Great Flood Prayer, LSB p. 269)

For we see how God in heaven pours out his grace through his Son’s baptism. Heaven, which before was closed, is opened by Christ’s baptism and a window and door now stand open for us to see through. No longer is there a barrier between God and us, since God himself descends at the Jordan. The Father lets his voice be heard, the Son sanctifies baptism with his body, and the Holy Spirit descends in the form of a dove. Is this not a great manifestation, a truly great sign of how precious baptism is to God, that he does not abstain from it?…

Thus the Godhead in all fullness, Father, Son, and Holy Spirit was manifested on this day in profoundest graciousness and friendliness, each person of the Trinity clearly distinguished, so that everyone might know what and how to believe concerning God, especially what his stance towards Christ should be. For whoever holds to Christ, accepts his Word, and trusts his work cannot be an enemy of God…

No doubt there were countless holy angels present. For where the Father, Son, and Holy Spirit reveal themselves, all the heavenly host must also be present. This was the ultimate manifestation. Therefore, learn to estimate this festival highly. The star given to the wise men was a manifestation, too, but this was much more wonderful. For here the three preeminent Kings—God the Father, God the Son, God the Holy Spirit—are all present…

Each and every sinner needs baptism so that his sins might be washed away; whoever is in death needs baptism that death might be swallowed up, for baptism has God-given power to cleanse from sin and bury death…

Even though we have fallen into sin and done wickedness, yet will our baptism and its promises remain firm and sure. Only, we need to repent and not persist in sinning. For these two things are mutually exclusive: to yearn for forgiveness and then cling to our sins and refuse to leave them.

(HP I:Epiphany, Third Sermon—1534, pp. 216ff.)