Here is the special authority of Christ Jesus, who does not simply teach the Holy Scriptures, but fulfills them in Himself. Here, for example, we find Him keeping the Sabbath (in more ways than one), and using the Name of God rightly.
There is the special authority of the Law, which exposes and exacerbates the unclean spirit in you, the perverse flesh of your old Adam in your thoughts, words and deeds. For you strive to live by the Law, but you cannot keep it. So you become angry and afraid. You flaunt it, or despise it, or despair of it. You are quick to criticize and condemn others, because you are convinced that God is out to get you.
After all, listen to His Law, to what it commands, forbids and threatens you. And consider that He is the Holy One, who requires that you must be holy and perfect. Trying hard is never enough. Anything less than perfect is sinful and unclean. So what does that mean for you? Why has He come with this authority of His? Is He here, and does He speak, to destroy you?
These are the questions, not of those who go ignorantly about their lives in the world, but of those in the synagogue, who are gathered together before God and confronted by His Word.
He is here on this Sabbath, and His presence throws you into convulsions, because His Word brings to light the war that is waged in your members, that is, within your sinful flesh.
There is this sense in which He must destroy you; He must condemn and crush and crucify you. For if you are not thus brought to contrition and repentance, then you are lost altogether.
But it is not finally for that purpose that He has come. Nor is that His special authority as the Son of Man, the incarnate God, the crucified and risen Lord Christ.
He removes the unclean spirit from you, and He restores a new and right spirit within you, not by violence, threats or punishments against you, but with forgiveness of all your sins. That is why He has come: He is here to forgive you, in order to give you life.
It is true that His preaching of repentance puts you to death, but it does so in order to bring you into life with Him.
That is what He has done for you in your Baptism. There you were crucified, dead and buried with Him; and thereby are you raised with Him to newness of life. There He poured out His Holy Spirit generously upon you, and into you; and so does He drive out the unclean spirit of your sin, your unbelief, your guilt and shame, your wicked perversion, your death and despair.
Do not be afraid.
Do not hide yourself away from Him.
Do not shut your ears to His Word, nor drown out His voice with your own chatter, your endless discussions and debates, your angry arguments and accusations.
Listen to Him.
Be quiet and at peace. Be still, and know that He is God, your Savior.
He has willingly, lovingly, gone to the Cross and died for your transgressions. You didn't have to talk Him into it; He chose to go and do it for you, because He loves you. And He has been raised for you, also, for your justification, your reconciliation with God (and with one another).
His preaching and authority, which are so threatening and scary to you, return you to the death and resurrection of your Baptism. Which is to say that He unites you to Himself in His dying and rising, so that you are not destroyed forever, but you are forgiven and saved.
That is why His Church is the true synagogue, and His Gospel is the true Sabbath. For by the authority of His Cross and Resurrection, in His Name, you are forgiven. Even your death cannot destroy you, and the devil cannot accuse you, because God does not count your sins against you.
You are forgiven. You are innocent. You are holy and righteous. You are alive. You are free.
In the Name + of the Father and of the Son and of the Holy Spirit. Amen.