When Jesus had driven out a demon, some of the crowd said: “By the power of Beelzebul, the prince of demons, he drives out demons.” Others, to test him, asked him for a sign from heaven. But he knew their thoughts and said to them, “Every kingdom divided against itself will be laid waste and house will fall against house. And if Satan is divided against himself, how will his kingdom stand? For you say that it is by Beelzebul that I drive out demons. If I, then, drive out demons by Beelzebul, by whom do your own people drive them out? Therefore they will be your judges. But if it is by the finger of God that I drive out demons, then the Kingdom of God has come upon you. When a strong man fully armed guards his palace, his possessions are safe. But when one stronger than he attacks and overcomes him, he takes away the armor on which he relied and distributes the spoils. Whoever is not with me is against me, and whoever does not gather with me scatters.
“When an unclean spirit goes out of someone, it roams through arid regions searching for rest but, finding none, it says, ‘I shall return to my home from which I came.' But upon returning, it finds it swept clean and put in order. Then it goes and brings back seven other spirits more wicked than itself who move in and dwell there, and the last condition of that man is worse than the first.”
As it was necessary for many reasons to refute the cavils of His opponents, our Lord now makes use of a very plain example, by which He proves to those who will consider it that He overcomes the power of the world, by a power inherent in Himself, saying, "When a strong man fully armed keeps his palace." He calls the devil "strong", not because he is so by nature, but referring to his former tyranny caused by our negligence. For he used to seize upon the flocks of God with great violence and carry them to his own fold before the coming of the Savior.
But the world the devil calls his palace, which lies in wickedness, wherein up to our Savior's coming he enjoys supreme power, because he rested in the hearts of unbelievers without any opposition. But with a stronger and mightier power Christ has conquered, and by delivering all men has cast him out. Hence it is added, "But if a stronger than he shall come upon him, and overcome, etc." For as soon as the Word of the Most High God, the Giver of all strength, and the Lord of Hosts, was made man, He attacked the devil, and took away his arms. His arms then are the craft and the wiles of spiritual wickedness, but his spoils are the men themselves, who have been deceived by him.
As conqueror, Christ too divides the spoils, which is a sign of triumph, for leading captivity captive He gave gifts to men, ordaining some Apostles, some Evangelists, some Prophets, and some Pastors and Teachers.
Catena Aurea (St. Thomas Aquinas)
Commentary on Luke, Sermon 81 (St. Cyril of Alexandria)
On the Gospel of Luke (St. Bede the Venerable)
Homily 41 on Matthew (St. John Chrysostom)