Who is this who's teaching with such authority? In Mark 1:21-39, we see that this person is Jesus, and with his arrival, he brings the reign of God, invades the kingdom of darkness, and sets people free from the bondage of satan, sin, and death. He not only proclaimed the kingdom of God, but also demonstrated it with real power. No matter what you're going through in your life, never forget that Jesus has authority over it.