And there was in their synagogue, &c.— It seems plain from what is said afterwards, Mark 1:27 that the other persons then present did not know Jesus to be the Son of God; how then should the demoniac know this, if he had been only mad, as some would vainly suppose, and not really possessed by an evil spirit? This case was so remarkable, that, as the Evangelist adds, immediately our Lord's fame spread abroad, throughout all the region round about Galilee. However, though madmen might not know Christ, yet the devils could not be ignorant of him, from the time of his baptism, when the voice from heaven said, This is my beloved Son, &c. and therefore Satan soon after, in one of his temptations, says, If thou be the Son of God; Matthew 4:6. See Ward's Dissertations, p. 79 and on Matthew 8:29.
Related Commentaries of Mark 1:23
Mark 1:23-24
23 And there was in their synagogue a man with an unclean spirit; and he cried out,
24 Saying, Let us alone; what have we to do with thee, thou Jesus of Nazareth? art thou come to destroy us? I know thee who thou art, the Holy One of God.