The Bible doesn't use the word "cult," but I know what you mean. Your question could be reworded as, "How do we know if a religious organization is not of God?"
The Bible teaches that there is one foundational truth that all religions must have. This is a belief in Jesus Christ as Savior and Lord, with no other way of salvation, except through Him. If any organization holds a different view, then they would Biblically be considered not of God and a cult. Let's review some Scripture that declares this truth.
Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son. Whosoever denieth the Son, the same hath not the Father: he that acknowledgeth the Son hath the Father also.The Bible states that a false religion or cult is one that doesn't acknowledge that Jesus, the Christ, (God or Messiah) came in the flesh and accomplished what the Bible declares. If this truth is not believed, then the religious organization is a cult. You will notice that many Christians who believe salvation comes through Jesus still have various views of the Bible. This happens because men are imperfect.
(1 John 2:22-23 KJV)
For many deceivers are entered into the world, who confess not that Jesus Christ is come in the flesh. This is a deceiver and an antichrist.
(2 John 1:7 KJV)
However, if we believe in Jesus, we are all part of one big family and we are told to love and accept each other (Rom. 14:1-23). When Jesus returns we will find out the entire truth and then we won't be so concerned about our differences.
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