Answer
Matthew 12 is a pivotal chapter in the narrative of Jesus’ earthly ministry and one that includes Jesus’ notable statement that “he who is not with Me is against Me, and he who does not gather with Me scatters abroad” (Matthew 12:30, NKJV).
Up to the point when Jesus says, “He who is not with Me is against Me,” He had been proclaiming the good news about the kingdom that He was offering, but in Matthew 12 He and His kingdom are rejected—particularly by the leaders of the nation. The situation comes to a head when Jesus heals a blind and mute man (Matthew 12:22). The crowds were in awe and were wondering whether He might be the Son of David, the Messiah (Matthew 12:23). The Pharisees, on the other hand, quickly rejected Jesus’ healing work as Messianic and instead asserted that Jesus had healed the man by demonic power (Matthew 12:24). Jesus challenged the absurdity of this critique and the failed logic of a divided kingdom and Satan fighting against Satan (Matthew 12:26–29). He then presented them with a dilemma, asking in whose power their sons cast out demons (Matthew 12:27). The point Jesus was making was that, if Jesus was casting out demons in the power of God, as He was claiming to do, then indeed the kingdom He was presenting had come because the King had come (Matthew 12:28).
Jesus then took it one step further by saying that “he who is not with Me is against Me.” The people had to make a choice. Their Messiah had come, offering to them the prophesied and covenanted kingdom of the heavens (which was ultimately God’s kingdom in the heavens come to earth in fulfillment of God’s covenant to David, with the Messiah ruling on David’s throne in Jerusalem). Jesus was the Messiah, and He was presenting His kingdom to the people. They had to choose—if they were for Him, they would have to change their mind (repent) about how they could gain entrance into the kingdom (Matthew 4:17). They would have to recognize that they could only enter the kingdom by the internal spiritual righteousness Jesus described, and not by their external obedience to the Law of Moses (Matthew 5—7). The Pharisees and other leaders were deeply opposed to changing their minds about these things; they could not accept that He was the Messiah, lest they have to submit to what He was telling them. Their rebellion illustrated Jesus’ statement that “he who is not with Me is against Me” (Matthew 12:30).
Like the Pharisees of that era, we also have a choice to make about Jesus. Jesus famously asked the question of His disciples, “But who do you say that I am?” (Matthew 16:15). Each one of us has to answer that question for ourselves. Either we acknowledge that He is who He said He is—the Messiah—or we reject that and attribute His words and works to something other than the true ministry of our Creator, Messiah, Savior, and King. With this choice there is no third option. Jesus did not give His listeners the option of avoiding the choice. “He who is not with Me is against Me,” He said. And if we claim to be for Him, then we must come to Him as He prescribes and not as we might prefer. The Pharisees were open to God’s involvement in their lives and the lives of the nation of Israel, but only on their own terms. As creations of the Creator, we don’t get to make the rules; we simply have to decide whether we are for Him or against Him.