John looked like he might be the Messiah, but God decreed that he would only prepare the way for the Messiah. Jesus didn't look like he could be more than just a lowly carpenter from Nazareth, but God decreed that he was his one and only son and that he was pleased with him. What we see in baptism looks like simple water, but God decrees that it is a washing of rebirth and renewal by the Holy Spirit. When we look in the mirror our eyes see a sinner deserving of God's punishment, but in connection with our baptism God decrees we are his dear children, washed by the blood of Jesus.