Jesus introduce this gospel passage by saying, “I have come to set the earth on fire, and how I wish it were already blazing!” The “fire” of which He speaks is His purifying fire of mercy that He poured forth from the Cross as He offered His life for the salvation of the world. His mercy is given to free us from our sins and to cleanse our souls so that God Himself can come to dwell within us. This is why we exist. God wants to dwell within us, and He wants us to be in perfect union with Him.
One of the glorious effects of uniting yourself to God is that this union also brings about a spiritual bond with others who are united to God. We are made for communion with God, but also for communion with each other. God especially invites family members to share in this unity. Though there are many levels of friendship and unity we can have with each other, the deepest bonds come from two souls each being united to God. For example, two people may both like the same sports team or have the same interests, resulting in a bond or form of friendship. This is good. But when each of those friends also is deeply united to God, the unity comes from God and not from something more superficial.
The challenging Gospel passage above reveals to us what happens when one or more members of a household fail to open themselves to the cleansing fire of God’s love and, therefore, fail to live in union with God. The result is disunity, at least on the deepest and truest level. God is not the cause of disunity; sin is. When one person is united to God and another is immersed in a life of sin, true spiritual unity is not possible. Of course the two might still share some common interests and might even superficially get along each day, but there will never be an experience of authentic spiritual friendship and communion if God is absent from one or both hearts.
When Jesus says that He has come to establish division within a household, He is simply pointing out that there will indeed be a division within a household when all are not united to God. Additionally, Jesus is warning us that if someone within our household tries to draw us into a life of sin with them, that person’s invitation must be rejected. And when that happens, that rejection is often experienced as a rejection of the person and results in even greater disunity. The bottom line is that it is not possible to be authentically united in sin or any form of lie.