When you talk about cults, most people have a few different images come to mind: Nike shoes, punch, hooded robes, and chants. While each of these characteristics stemmed from well-publicized real life situations, a cult involves a lot more than just strange practices and news headlines.
By definition, a cult is solely a sect or religion that is considered extremist, unorthodox or false. Followers of these sects often live out strange practices under the direction of a leader who tend to be very charismatic. Usually, the leader also claims to have some exclusive insight into their faith or a special connection to God.
Because it is unlikely that any group would self-describe as a cult, it is hard to apply this definition without the denial of the adherents to the group. For this reason, it is often best to look at the core beliefs in Christianity and to use those as the measuring rod for orthodoxy: who God is; who man is; and what their relationship is.
Who is God? A simple reading of the Bible and an understanding of how it has been interpreted throughout the ages gives you some standards by which to gage different groups. Some of the attributes that the Bible reveals about God include that he is eternal (without beginning or end) (Psalm 90:2, 1 Tim. 1:17), separate from Creation and self-existent (Ex. 3:14), sovereign (Dan. 4:5; Psalm 115:3), and Holy (Lev. 11:44).
Most cults deny one or all of these attributes. They believe that God is a created being (like the Jehovah's Witnesses) or achieved his godhood (such as the Church of Jesus Christ of Latter-day Saints).
Who is man? This question may be closely connected with the first. In Christianity, man is a created being (Gen. 1-2), separated from God because of sin (Romans 6:23), sinful by nature (Psalm 58:3), and unable to repair the broken relationship with God based on our own merits.
In Christian cults, man is often portrayed as not being so bad. Instead of being wretched and sinful, man is described as only needing a little help. A key phrase used in LDS script ure and quoted and explained by many LDS scholars such as Dr. Robert Millet (a professor at Brigham Young University and an adherent of the Church of Jesus Christ of Latter-day Saints) in a his book "Grace Works": "For we labor diligently to write, to persuade our children, and also our brethren, to believe in Christ, and to be reconciled to God; for we know that it is by grace that we are saved, after all we can do." This philosophy renders Jesus' sacrifice as just filling in the gap where we were unable to complete the task, instead of being a complete redemption of a sinful people.
Once you have a good sense of the church/cult/denomination's views on these three issues, for the most part you can easily discern whether the group is a legitimate branch of Christianity, a cult, or something more divisive. The differences that exist between the denominations of Christianity tend to be oriented toward tradition, personal style, and culture. For example, the Lutheran Church tends to have a formal, traditions-based worship style. Inter- or non-denominational churches will often be a mixture of different styles and will define themselves by their ability to reach out to people from many different denominations or traditions.
Denominations are not a bad thing in themselves. One way to think about them is that they each accentuate a different attribute of God. Presbyterians often cite that "God is a god of order, not of chaos." This is lived out through their Book of Order, committee-based system, and leadership structure. Ultimately, each church will have their own style and traditions, while staying true to the key beliefs articulated above.
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