‘And the unclean spirits, whenever they beheld him, fell down before him and cried out saying, “You are the Son of God”. And he strongly charged them that they should not make him known.'
And as a result the ‘battle' with Satan continued. Whenever unclean spirits saw Him they could not help but cry out in fear that He was ‘the Son of God' and cause their host bodies to fall down before Him. But He did not want their testimony to Him. It would not produce the right reactions. So He silenced them as was His usual custom. In Mark ‘Son of God' is an outright testimony of deity. This was not only the time of positive salvation but of the wholesale defeat of the forces of evil. Note how the discerning forces of evil know Jesus for Whom He is, in direct contrast with the experts from Jerusalem who totally misrepresent Him (Mark 3:22). But neither of them benefit by it because they do not want to follow Him. ‘The devils also believe and tremble' (James 2:19).
Each of these factors will shortly be illustrated by outstanding examples, the preaching in Mark 4:1-34, the healing in Mark 5:21-43 and the casting out of evil spirits in Mark 3:22-30; Mark 5:1-20, but first it was necessary to establish why He had come. The appointing of the twelve which now follows was a visible indication that the Kingly Rule of God was now present and thus required its authoritative leadership to be appointed (but as servants of all).