The meaning of the example is this: The devil is the strong man; his goods are the men into whom he is received; unless therefore a man first conquers the devil, how can he deprive him of his goods, that is, of the men whom he has possessed? So also I who spoil his goods, that is, free men from suffering by his possession, first spoil the devils and vanquish them, and am their enemy. How then can ye say that I have Beelzebub and that being the friend of the devils, I cast them out?.
We must however understand, that they will not obtain pardon unless they repent. But since it was at the flesh of Christ that they were offended, even though they did not repent, some excuse was allowed them, and they obtained some remission.