A job given to the witness in a court trial is to bring out personal knowledge about the accused. It may sway the jury one way or another. A typical question may well be “Is the accused individual generally a good or bad person?” Personal knowledge is very important in witness evaluation.
In the Gospel for the Third Sunday in Advent (Luke 3:10-18), John the Baptist is a “witness” so has much to say about Jesus. We can assume that John was well aware of much that Jesus was teaching and so was able to share it with others. John was effectively preaching to a crowd . I suspect that the crowd wanted to be baptized and thus “become” clean.
Different groups basically asked the same question: “What can I do?” John’s basic response was one of sharing with others. He also pointed out that Tax collectors were told not to collect more than what is due. Soldiers were told not to practice extortion nor to falsely accuse anyone.
Quite likely the people were moved by what John had said and wanted to be baptized by him so as to be thoroughly cleansed. Then, John began to “witness” Jesus. “Baptism” as a cleansing agent is what the people wanted, and John made a specific distinction between his baptism and that of Jesus.
John’s baptizing was with water only. Jesus would baptize with the “Holy Spirit” and “fire.” No doubt a strange combination. Most likely, “fire” came from a later Tradition which referred it to Pentecost, thus making Jesus’ Baptism a plan of “action” fueled by the Holy Spirit. (“Spirit” from the Hebrew [ruah] can also be translated as”power.”)
That is to say that for Jesus, the Baptism is basically a plan of action as exemplified by Jesus’ disciples at Pentecost who went out and preached Jesus’ message. God’s Spirit (“power”) is what made this possible.
What does this mean ? John was a witness testifying to the reality of Jesus’ teaching. For example, justice, compassion, forgiveness among other things (summaries found in Matthew chapters 5-7). Displaying our Baptismal responsibilities is a form of accepting Jesus’ teaching.
The fact is , if we display our Baptismal responsibilities consistently, then others will notice and become aware that there is truth regarding our “witness” program. That is to say, live what you believe.