When a bank teller is taught to identify counterfeit money there are some steps that must followed in order to know the difference between real and fake money.
In 1 John 2, the apostle John helps to protect believers from heresy by illustrating examples of counterfeit Christians and teachers. One of the signs of the last days is the arrival of the antichrist. Antichrists are those who claim to have His power and authority but don't, or those who reject and oppose Him and His teachings.
John gave three examples of false teachers who are controlled by the spirit of the antichrist. They depart from the fellowship, they deny Jesus as the Messiah, and they draw the faithful away from Jesus. He encouraged believers to protect themselves against the spirit of the antichrist by depending on the indwelling presence of the Spirit, knowing the truth, and remaining in fellowship with Jesus.