Jamieson, Fausset and Brown on Mark 1:34

34. And he healed many that were sick of divers diseases, and cast out many devils--In Mt 8:16 it is said, "He cast out the spirits with His word"; or rather, "with a word"--a word of command.

and suffered not the devils to speak, because they knew him--Evidently they would have spoken, if permitted, proclaiming His Messiahship in such terms as in the synagogue; but once in one day, and that testimony immediately silenced, was enough. See on Mr 1:24. After this account of His miracles of healing, we have in Mt 8:17 this pregnant quotation, "That it might be fulfilled which was spoken by Esaias the prophet, saying (Is 53:4), Himself took our infirmities, and bare our sicknesses."