How did Christ fulfill the righteousness of baptism? Without a doubt according to the demands of human nature: people need to be baptized, for according to carnal nature they are all sinners. [Jesus] fulfilled also the righteousness of being born and growing, of eating and drinking, of sleeping and relaxing. He also fulfilled the righteousness of experiencing temptation, fear, flight, and sadness, as well as suffering, death, and resurrection: that is, according to the requirement of the human nature he took upon himself, he fulfilled all these acts of righteousness.

—Anonymous, Incomplete Work on Matthew, Homily 4

[At Jesus’ baptism] then we have the Trinity presented in a clear way: the Father in the voice, the Son in the man, the Holy Spirit in the dove. This ineffable Divinity, abiding ever in itself, making all things new, creating, creating anew, sending, recalling, judging, delivering, this Trinity, I say, we know to be at once indescribable and inseparable.

—Augustine, Sermon 2.1-2