In the New Testament, there is question of an evil spirit, Beelzeboul. On account of the great similarity of names, he is usually identified with Baalzebub, beel being the Aramaic form of baal, and the change from the final b to l such as might easily occur. But there were numberless names for demons at that time, and this one may have been newly invented, having no relation to the other; the fact that one element of the compound is Aramaic and the other Hebrew would not disprove this. The meaning of the term is "lord of the mansion" or dwelling, and it would be supposed by the Jews of this time to refer to the nether regions, and so be an appropriate name for the prince of that realm. Beelzeboul (Beelzebub) is used, then, merely as another name for Satan (Matthew 12:24-29; Luke 11:15-22) by whom the enemies of Our Lord accused Him of being possessed and by whom they claimed He cast out demons. Their charge seems to have been that the good Our Lord did was wrought by the Evil One in order to deceive, which Jesus showed to be absurd and a wilful blindness. If the New Testament name be considered a transformation of the old, the question arises as to how the god of the little town of Accaron came to give a name to the Prince of Darkness. The mission on which Ochozias sent his followers seems to show that Beelzebub already had a wide renown in Palestine. The narrative (2 Kings 1) was a very striking one, well known to the contemporaries of Our Lord (Luke 9:54); from it might easily be derived the idea of Beelzebub as the special adversary of God, and the change in the final letter of the name which took place (ex hypothesi) would lead the Jews to regard it as designating the prince of the lower regions. With him was naturally connected the idea of demoniacal possession; and there is no need of Cheyne's conjecture that Beelzebub's "name naturally rose to Jewish lips when demoniacal possession was spoken of, because of the demoniacal origin assumed for heathen oracles". How can we account for the idea of Beelzebub exorcizing the demons? On the assumption that he is to be identified with the Philistine god, Lagrange thinks the idea is derived from the special prerogative of Beelzebub as fly-chaser (chasse-mouche). In the Babylonian epic of the deluge, "the gods gather over the sacrificer like flies" (see Driver, Genesis, 105). It was easy for the heathen Semites, according to Lagrange, to come to conceive of the flies troubling the sacrifice as images of spirits hovering around with no right to be there; and so Beelzebub, the god who drove away the flies, became the prince of demons in whose name the devils were exorcised from the bodies of the possessed. Others think the idea naturally arose that the lord of the demons had power to command them to leave the possessed. It seems much more reasonable, however, to regard this faculty of Beelzebub not as a tradition, but simply as a change invented by Our Lord's enemies to throw discredit on his exorcisms. His other miracles were probably accounted for by ascribing them to Beelzebub and so these likewise. Allen (Comm. on Matt., 107, 134) has endeavored to simplify the problem by the use of higher criticism. According to him, the role of Beelzebub as arch-demon and exorcist was not a Palestinian belief; in Mark's Gospel, Beelzebub is simply the demon said to possess Our Lord. Matthew and Luke by mistake fuse together two independent clauses of Mark 3:22 and identify Beelzebub and Satan, to whom the faculty of exorcism is ascribed. The fusion, however, seems to be justified by the next verse of Mark, which is more naturally interpreted in the sense of Matthew and Luke, though Allen's interpretation may be admitted as possible. Beelzebub does not appear in the Jewish literature of the period; there we usually find Beliar (Belial) as an alternative name for Satan.
Grabbed from http://www.newadvent.org