Luke uniquely indicated that Jesus said that when a strong man (ὅταν ὁ ἰσχυρὸς), fully armed (καθωπλισμένος), guarded his castle (φυλάσσῃ τὴν ἑαυτοῦ αὐλήν), his property or possessions would be safe and at peace (ἐν εἰρήνῃ ἐστὶν τὰ ὑπάρχοντα αὐτοῦ). Both Mark and Matthew have the attack on the house that is in the next verse, but without the setup of guarding the castle as here in Luke. How do you guard your house or castle?
Interesting enough, Sirach talked about the king who led the Israelite northern kingdom, who was not in the Davidic line of kings. Sirach was very harsh in his judgment about the northern rebels. Their kingdom was in fact called Israel, while the southern kingdom was called Judah. Jeroboam the son of Nebat was from Ephraim, just north of Judah and Benjamin. He actually had worked for Solomon in his administration, as indicated in 1 Kings, chapters 11-14. A prophet told Jeroboam that he would be king. After a meeting with Rehoboam, Jeroboam set up a new kingdom at Shechem. His great sin was that he did not want the people to go to Jerusalem to worship. Thus he setup his own worship places. This false worship led to the downfall of the northern Kingdom of Israel (721 BCE) before that of the Kingdom of Judah (587 BCE). The wickedness of this kingdom deserved the vengeance that came to it.