The relationship between the teachings of Christ and many so-called Christian religions (historically and vaguely called “Christianity”) is similar to the relationship between the scientific method and science as a belief system (scientism).
He [Jesus] replied, “Isaiah was right when he prophesied about you hypocrites; as it is written: ‘These people honor me with their lips, but their hearts are far from me. They worship me in vain; their teachings are merely human rules.’ You have let go of the commands of God and are holding on to human traditions.” And he continued, “You have a fine way of setting aside the commands of God in order to observe your own traditions!”
Mark 7:6-9 (NIV)
In both cases, a label is used to make a linguistic association with true principles, but the core of what people claim as their foundation is far from their understanding and intent; they organize and act based on appealing to their own traditions and authority instead. In other words, labels like “Christian” and “science” become mere brands that they use to manage perceptions and promote their own agendas.
If you disagree with their cult of authority, you are accused of rejecting the namesake of their brand. To question a person in a position of religious authority is treated as a rejection of God. To question a person in a position of (politically) scientific authority is to reject science itself.
Whether or not there are good reasons to doubt them or other authorities who disagree with them is brushed aside. They decide what the messaging of the brand will be. You agree with and obey the cult’s chosen or you are a heretic, truth be damned. And sooner or later, authorities insist that heretics must be shunned, exiled, or killed. If people listen to heretics, they may stop giving attention and money to the cult, you see.