He didn't know what would happen after he spoke. He knew what he was called to say.
John 1:19β23
"Who are you?" He did not fail to confess, but confessed freely, "I am not the Messiah." They asked him, "Then who are you? Are you Elijah?" He said, "I am not." "Are you the Prophet?" He answered, "No." Finally they said, "Who are you? Give us an answer to take back..." John replied in the words of Isaiah: "I am the voice of one calling in the wilderness, 'Make straight the way for the Lord.'"
Which part of John's answer speaks to something you are wrestling with in your own calling?