Albert Barnes Commentary Mark 3:11-12

"And the unclean spirits, whensoever they beheld him, fell down before him, and cried, saying, Thou art the Son of God. And he charged them much that they should not make him known." — Mark 3:11-12 (ASV)

Unclean spirits. Persons who were possessed by evil spirits.

Thou art the Son of God. The title "Son of God" is used here in a preeminent sense. In this context, it is equivalent to "the Messiah," a title by which the Son of God was known among the Jews.

Therefore, they were instructed not to make Him known, because He did not desire it to be widely proclaimed that He claimed to be the Messiah. He had not yet accomplished what He intended to establish His claims to the Messiahship; He was poor and without honor, and the claim would have been treated as that of an impostor (as it later was), and would have endangered His life. For the present, therefore, He did not wish it to be widely proclaimed that He was the Messiah.

This circumstance proves the existence of evil spirits. If these were merely diseased or deranged persons, then it is strange that they should be endowed with knowledge so far superior to that of those in health. If they were under the influence of an order of spirits superior to man—whose proper dwelling place was in another world—then it is not strange that they should know Him, even in the midst of His poverty, to be the Messiah, the Son of God.