“And they went into Capernaum, and straightway on the sabbath-day He entered into the synagogue and taught. And they were astonished at His doctrine, for He taught them as one that had authority, and not as the scribes.” This is the first and essential point in the ministration of God’s word, that it should be spoken with authority. Flesh may imitate it. The world thinks that self-will is the only thing that can avail to effect any end. But, however strong man’s will may seem in the things of men, the certainty of God’s will is the one thing by which the Holy Spirit clothes the word with authority in divine things. This was preeminently the case with Christ, for He alone as man had the Lord always before Him. But even with us there should be the speaking with assurance of God’s mind and will (1 Peter 4:11), if we speak for God at all; otherwise it would be better to be silent. With the scribes it was not so. They may reason or they may dazzle, as argument or fancy preponderances. But for us, it is better not to speak if we have not the certainty of that which God would have spoken at any given time. By speaking uncertainly, we only communicate our own doubts and darkness to others. But if we have by grace the certainty of God’s truth, let it be spoken with authority. It is as servant that Christ does so here. He was Himself the perfection of humility; for it is in no way inconsistent with a lowly mind to speak with the fullest authority where we have no doubt about the mind of God. 

An Exposition of the Gospel of Mark - William Kelly