In this verse Jesus makes explicit application of the parables of the divided country and the divided family of verse 25. This can be made explicit in the translation by beginning the verse “In the same way…” or “Thus it is that if Satan….”
In the clause if Satan casts out Satan, it is clear that the name of the leader of the group, Satan, is used to represent either one of Satan’s demons or a group of Satan’s demons. This is the basis for Good News Translation: (“So if one group is fighting another in Satan’s kingdom”) and Bibel im heutigen Deutsch, 1st edition (“If one demon is casting out the other, then Satan would be fighting against himself”). It is absolutely necessary that the readers be made to understand that Satan of this verse is the same person as Beelzebul of verses 24 and 27. It may be good to have a footnote saying that Satan and Beelzebul are two names for the same person. Another way to help readers make the identification is to expand the Bibel im heutigen Deutsch, 1st edition model: “If one evil spirit of Satan’s kingdom is casting out another, then Satan would be fighting against himself.” For further comments on Satan, see 4.1, 10.
How then will his kingdom stand? is a rhetorical question in Greek and is translated by Good News Translation “this means that it is already divided into groups and will soon fall apart!” An adequate and accurate translation of this verse may require much restructuring: “If what you say about me is true, then this shows that Satan’s kingdom is already divided into groups. One group is fighting against another, and so his kingdom will soon fall apart.” Or, patterned after Bibel im heutigen Deutsch, 1st edition, “You say that I am using Satan’s power to cast out demons. This means that Satan is fighting against himself, and so his kingdom will not last much longer.” A variation is “If one member of Satan’s kingdom is casting out another, which is what you say is happening when I cast out evil spirits, then Satan is fighting against himself, so his kingdom will soon be destroyed.”
Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .