Parallel passages: Mark 3:27; Luke 11:21, Luke 11:22. Mark is practically identical with Matthew. Luke ("the strong man armed," etc.) is more detailed and vivid, and is perhaps the original form of the saying.
Or else; or (Revised Version); i.e. if this be not the case, that the kingdom of God is come upon you, how else do you explain what has happened, the fact of Satan's instruments being taken from him?
How can one enter into a strong man's house; the house of the strong man (Revised Version). (For the article, cf. Matthew 1:23, note.) And spoil ( ἁρπάσαι) his goods. Carry off his household tools and utensils ( τὰ σκεύη αὐτοῦ).
Except he first bind the strong man? and then he will spoil his house. This is more than merely the conclusion. It is an emphatic statement that tie will do this, yes, utterly plunder ( διαρπάσει) the whole house.
The interpretation of the parable is self-evident: the strong man is Satan; his vessels are those afflicted by him; the one who binds, etc., is Christ. For Christ's appearance and work, even before the Crucifixion and Resurrection, bound Satan in this respect.
Observe that there is probably a tacit reference to Isaiah 49:25, which at any rate now received a fulfilment.