“For I came to set a man at variance against his father,
And the daughter against her mother,
And the daughter in law against her mother in law,
And a man's foes will be those of his own household.”
(Note the pattern, which will be repeated again twice below, a threefold statement followed by a conclusion).
The sword will divide and even slay. But the picture here is not of warfare. It is of a world at war with Christ. ‘At variance' does not in itself signify fighting. It signifies being in disagreement with and having different conflicting views. The fighting comes from the other side, and from their reactions. The idea is that the belligerence that results will all be on the side of the opposing family members. It is they who will become the ‘foes' of the disciple, not he of them. But Jesus' warning is that often that will be the sad result of a disciple believing the truth and holding to it, as he must. But there is no thought here of him fighting back.
For fighting in the name of Christ is never justified. When men choose to go to war for what they believe in, they do not do it as Christians, even though sadly they may often have thought that they did so. It is true that Christians may have to fight in order to defend themselves and their families and allies against attack. They have a right to defend themselves. But they should never fight in order to defend what they believe in. That should be ‘fought for' by revealing love and suffering for Christ's sake.
So the point here is that by receiving the truth and believing in Christ, men and women will find themselves disagreeing with their families in a spirit of love, but will often find in return that the reaction will be a spirit of hate, because of the strong feelings involved as a result of cherished ideas being set at nought. In this case the following of Christ will be seen as an attack on the old beliefs, and may result in difficulties, persecution or even worse, as He has already warned (Matthew 5:10-12). And it is at that point that the crunch choice will have to be made.
The relationships described are the deepest known to man, and were sacred to the Jews. A man must honour and respect and give filial obedience to his father. It is central to the covenant (Exodus 20:12). A daughter must honour and respect her mother who, until she is married, rules the female side of the family. A daughter-in-law must honour and respect the one who has become to her as a mother in the place of her own mother. And Jesus agreed with all three principles. But nevertheless when it came to honouring them or honouring Him, He must come first. Loyalty to Him outranked the all. For as He will now point out, their love and respect for Him must exceed that for their dearest and closest relatives. While the Rabbis to some extent put the Teacher in a more exalted place than the father, they would never have been as extreme as this.