I apparently understand it far better than you do. Jesus was establishing the premise for His own authority to cast out demons. In the preceding verse He said:
"If Satan casts out Satan, he is divided against himself; how then will his kingdom stand? - Matthew 12:26
He completes His argument establishing His authority in the very next verse:
"But if I cast out demons by the Spirit of God, then the kingdom of God has come upon you." - Matthew 12:28.
I’m tempted to comment but won’t other than “well said.”
Man made teachings/traditions nullify God’s Word. Satan’s tactic from the beginning was to nullify God’s Word.
So who do participants in man made teachings think they are casting out with exorcism prayers for those who believe in God’s WORD ONLY ? LOL!! No one can cast out the Holy Spirit from God’s WORD ONLY believers.
Catholics already invited satan in with embracing man made teachings/doctrines/traditions.
God’s Holy Spirit inspired WORD reigns. God’s Word is the FINAL AUTHORITY. IT ALWAYS was and ALWAYS will be!
There is NOTHING satan can do about it but he tries by deceiving others with man-made counterfeit teachings that oppose God’s Word. His only weapon is deception. Nothing new under the sun.
Apparently you do NOT understand it, at all. Jesus was talking to the Pharisees, you know those people He said were of their father, the devil?
Pharisees practiced exorcism, thinking they were casting out demons for God. But the Pharisees were of their father, the devil. Jesus named their practice to disprove their accusation about Him. If you and your disciples cast out demons, then it proves that you are also of the devil. (v. 27-28).
So sorry you missed His whole point. People who are not saved thinking they are doing God's work, when they don't even know God, are casting out demons by their father, the devil. And thinking because they do good works for righteousness, their exorcisms MUST be God's work.
They fell for it then. They are falling for it today. Satan can cast out all the demons he needs to keep someone blind and lost. Know any religion who believe their works are their righteousness, who practice exorcism, and think God is behind their "success"?