Some Christians accept teachers simply because they say "Jesus is God" or they "have faith in Jesus". It seems rare that Christians actually obey the command of Jesus to "test the spirits" (1 John 4:1). Not testing the spirits can lead us down the road to apostasy and shipwreck our faith.
Here is a great example. The Jehovah's Witnesses, on their official ministry page (www.jw.org), claim that "Jesus is the Son of God". To most Christian observers, this would be "enough" to "follow" their religion and go to their church. Some may believe that the JW's are Christian because they have the "essential doctrine" (of Jesus being the Son of God) covered. The Word gives no distinction between essential doctrines and non-essential doctrines, in fact, all of Scripture is God-breathed (2 Timothy 3:16) and we must not pick and choose which words Christ said that were essential or non-essential. Titus 2:1 says, "You must teach what is in accord with sound doctrine". Christ spoke of sound doctrine quite frequently and stressed the importance of hearing and doing His words in many places throughout scripture including the Parable of the Wise and Foolish Builders. If it came out of His mouth, every word is essential. When the faithful Christian goes further and digs deeper and really "tests" the spirits, there is way more to be found.
The Jehovah's Witnesses explain on the questions page:
The Bible identifies why Jesus has had a greater impact than any other good man who ever lived. When Jesus asked his closest followers who they thought he was, one of them correctly answered: “On another questions page, they even tell others that they are Christians:You are the Christ, the Son of the living God.”—Matthew 16:16.
Yes. We are Christians for the following reasons:To most readers, this would seem to be a Christian organization. But when one digs deeper, they deny essential Christian doctrines like hell, the Trinity, and Christ's dual natures after His resurrection to name a few.
Likewise, Bethel Church says sozo is a Christian practice. They claim to be a Christian church. Bill Johnson says that Jesus is eternally God, just like the Jehovah's Witness religion says Jesus is the Son of God. Everything looks peachy on the surface, but what do you see when you dig deeper? James 2:19 says that the demons also believe there is one God. The Greek word for believe is pisteuo. The definition of this word is to have faith in/to believe in (click on hyperlink on word to view the Greek Concordance)! This is the same word used for believe in John 3:16.
Some have said, if a church says they believe in Jesus than that is good enough for me! What they do not realize is that the doctrine must be "sound" or correct to be a true Christian church. Jesus said you will know them by their fruit (Matthew 7:20). The Bible says that truth is a fruit (Ephesians 5:9).
Remember in Matthew 16 when Jesus warned His disciples of unsound doctrine (bad leaven)?
5 Now when His disciples had come to the other side, they had forgotten to take bread. 6 Then Jesus said to them, “Take heed and beware of the leaven of the Pharisees and the Sadducees.”7 And they reasoned among themselves, saying, “It is because we have taken no bread.”8 But Jesus, being aware of it, said to them, “O you of little faith, why do you reason among yourselves because you have brought no bread?[c] 9 Do you not yet understand, or remember the five loaves of the five thousand and how many baskets you took up? 10 Nor the seven loaves of the four thousand and how many large baskets you took up? 11 How is it you do not understand that I did not speak to you concerning bread?—but to beware of the leaven of the Pharisees and Sadducees.” 12 Then they understood that He did not tell them to beware of the leaven of bread, but of the doctrine of the Pharisees and Sadducees.How important it is to come to know how tricky and deceptive satan is. Remember what the Apostle Paul told the Corinthians?
Oh, that you would bear with me in a little folly—and indeed you do bear with me. 2 For I am jealous for you with godly jealousy. For I have betrothed you to one husband, that I may present you as a chaste virgin to Christ. 3 But I fear, lest somehow, as the serpent deceived Eve by his craftiness, so your minds may be corrupted from the simplicity[a]that is in Christ. 4 For if he who comes preaches another Jesus whom we have not preached, or if you receive a different spirit which you have not received, or a different gospel which you have not accepted—you may well put up with it! 5 For I consider that I am not at all inferior to the most eminent apostles. 6 Even though I am untrained in speech, yet I am not in knowledge. But we have been thoroughly manifested[b] among you in all things. 7 Did I commit sin in humbling myself that you might be exalted, because I preached the gospel of God to you free of charge? 8 I robbed other churches, taking wages from them to minister to you. 9 And when I was present with you, and in need, I was a burden to no one, for what I lacked the brethren who came from Macedonia supplied. And in everything I kept myself from being burdensome to you, and so I will keep myself. 10 As the truth of Christ is in me, no one shall stop me from this boasting in the regions of Achaia. 11 Why? Because I do not love you? God knows! 12 But what I do, I will also continue to do, that I may cut off the opportunity from those who desire an opportunity to be regarded just as we are in the things of which they boast. 13 For such are false apostles, deceitful workers, transforming themselves into apostles of Christ. 14 And no wonder! For Satan himself transforms himself into an angel of light.15 Therefore it is no great thing if his ministers also transform themselves into ministers of righteousness, whose end will be according to their works. (2 Corinthians 11)