Mar 3:23 How can Satan cast out Satan?
Alternative: By what means can adversity eject adversity?
Did Christ see "Satan" as a real person or did he, as the Hebrew word is generally interpreted in the Jewish tradition, use the term to address the nature of adversity? In this verse and those that follow, we get a clearer idea.
Elsewhere, Christ refers to the personalization of evil with the term Beelzebub (Beelzeboul). This discussion always starts, as it does here, with his opponents using that concept. In response, Christ refers to others using the term (and the concept), aiming it at him as a person:
"If they have called the master of the house Beelzebub..." (Mat 10:25)
"And if I by Beelzebub cast out devils..." (Mat 12:27) (Luk 11:19)
"...ye say that I cast out devils through Beelzebub." Luk 11:18
For Christ, the problems of adversity make much more sense when we take the "persona" of Satan out of the equation. Christ is trying to explain that the approach of identifying adversity as a group of demons, headed by a chief demon, as used by his opponents, doesn't make sense. In the next few verses, he makes this point specifically, as the Gospel writer explains, by analogy ("parables," parabole). In this verse, he starts by saying that while a person might have the authority over others who are subject to him that doesn't make sense if you address reality as it is. It isn't caused by a hierarchy of demons who can be ordered around. Adversity isn't a person. It is a fact of nature.
For Christ, his "authority" over physical disease and mental disorder is identical. In line with his general teaching, both forms of disability arise from a natural, if spiritual cause. While in the modern era, we may see "nature" as solely materialistic, but Christ's view was that the physical was only what was apparent while the spiritual is what hidden, at least temporarily. The spiritual is what persists over time. (Note: While those with mental problems are described in the Gospels as "having demons," this usage is the same as modern expressions where we describe people as battling their "inner demons." ) His authority over people's disabilities and inner demons comes from the "Holy Spirit" that addressed adversity.
For Christ, the concept of adversity persists eternally even though individual instances of adversity come and go. An individual adversary, say a thief (as used later in this verse), might be stopped by another adversary, say a competing thief, but this does not destroy the nature of adversity itself. This anthropomorphizing of adversity takes us away from what Christ is trying to explain about what is really going on in the universe.
"Cast out" is from ekballô (ekballo) and means "throw out", "cast out of a place,"and "expose." Ek means "out of", "from," and "away from." Ballo is "to throw" or "to scatter." The general idea of ballo is "to throw without caring where something falls," so it isn't like putting something into a specific place. This term is always used when Christ speaks of casting out spirits or ejecting someone from a place where they are unwanted.
"Satan" is from satan (satanus, satan), which means "adversary", "opponent," and
"accuser." These are Hebrew origin words, appearing in Greek only in the New Testament. The traditional Jewish view does not portray "satan" as an evil angel (explanation here). A case can be made that our personalization of Satan is largely an artifact of incomplete translation.