John Gill

And they were all amazed,.... The people in the synagogue; they were astonished at his doctrine before, and now at his miracles: and spake among themselves; as they were in the synagogue, what a word is this? meaning, either what sort of doctrine is this which is attended with such power and miracles; or what a word of command is this, "hold thy peace, and come out of him?" and so the Ethiopic version renders it, "what is this mandatory", or "commanding word?" to which agrees the Syriac version, rendering it with the following clause thus; "what is this word", that "with authority and power it commands the unclean spirits, and they come out?" See Gill on Mar 1:27.