John Calvin Commentary Mark 5:9

"And he asked him, What is thy name? And he saith unto him, My name is Legion; for we are many." — Mark 5:9 (ASV)

My name is Legion. The devil was compelled by Christ to pronounce this word, that he might more fully display the greatness and excellence of his grace. There must have been good reasons why this man endured so severe a punishment as to have an army of devils, so to speak, dwelling within him. What compassion, then, it was to rescue from so many deaths a man who was more than a thousand times ruined! It was a magnificent display of the power of Christ, that by his voice not one devil, but a great multitude of devils, were suddenly driven out. Legion denotes here not a definite number of men, but merely a great multitude.

Hence it is evident what a wretched creature man is, when he is deprived of divine protection. Every man is not only exposed to a single devil but becomes the retreat of vast numbers. This passage also refutes the common error, borrowed by Jews and Christians from the pagans, that every man is attacked by his own particular devil. On the contrary, Scripture plainly declares that, just as it pleases God, one devil⁵⁵⁴ is sometimes sent to punish a whole nation, and at other times many devils are permitted to punish one man; as, on the other hand, one angel sometimes protects a whole nation, and every man has many angels as his guardians. There is the greater necessity for keeping diligent watch, lest so great a multitude of enemies take us by surprise.

⁵⁵⁴ “A scavoir que chacun hornroe ha son diable et son mauvals ange qui lui fait la guerre;” — “namely, that each man has his devil and his evil angel who makes war with him.”;” — “namely, that each man has his devil and his evil angel who makes war with him.”