Not only is testing the spirits to see whether they are from God commanded by the Lord in His word but is also commended by the Lord in His word – “I know your deeds and your toil and perseverance, and that you cannot tolerate evil men, and you put to the test those who call themselves apostles, and they are not, and you found them to be false” (Revelation 2:2).
1 John 4:1-6 is very pertinent and potent in testing the spirits to determine whether they are from God. However, if we don’t keep the whole paragraph in its immediate context along with the overall context of Scripture, we may fail to understand how these deceivers are to be spotted. At first glance this passage seems to be saying that anyone who professes that Jesus Christ has come in the flesh is from God. That is not what it is saying! Overall context of Scripture and the immediate context of this passage points out clearly that professing Jesus as coming in the flesh and as Lord isn’t the same as confessing that Jesus Christ has come in the flesh and is Lord.
The word “confess” is homologeo, from homos, “the same,” and lego, “to speak,” and therefore “confess” means to “speak the same thing as another.” This means that to confess Jesus Christ as coming in the flesh is to be actuated by the Holy Spirit of God and to say the exact same thing about the person and work of Christ that God Himself says. This is more than profession and head knowledge; this is confession and is heart knowledge. This confession of Jesus Christ coming in the flesh is to move into the realm of illumination concerning penal substitution and the exclusivity of salvation in Jesus Christ alone based on His sinless life, death for sinners, and resurrection from the dead for the purpose of the imputation of righteousness to the unrighteous whereby God can be both just and the justifier of those who have faith in Jesus Christ. This is clearly enunciated in Romans 10:9-10 – “that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved; for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation.”
Jesus also addressed the issue of those who profess Him but do not really confess Him in Matthew 7:21-23 – “Not everyone who says to Me, ‘Lord, Lord,’ will enter the kingdom of heaven, but he who does the will of My Father who is in heaven will enter. Many will say to Me on that day, ‘Lord, Lord, did we not prophesy in Your name, and in Your name cast out demons, and in Your name perform many miracles?’ And then I will declare to them, ‘I never knew you; DEPART FROM ME, YOU WHO PRACTICE LAWLESSNESS.’”
Notice that these false prophets of whom Jesus was speaking professed Him as Lord but didn’t abide by the Word of God doing His Father’s will. Instead they practiced lawlessness; they were workers of iniquity – twisting the Scriptures to their own destruction. This brings us back to 1 John 4:1-6 where John went on to say that the many false prophets who have gone out into the world speak as from the world and the world listens to them. How do we know if someone is just professing Christ as Lord and is a false prophet or if he is confessing Christ as Lord and is a true prophet? The answer is in whether or not he twists the Scriptures and speaks as from the world in order to be heard by and listened to by the world or whether or not he is true to the Scriptures and speaks as from God with the world rejecting his message.
If what a man teaches violates Scripture then he is a false prophet regardless of his profession of Jesus because right belief (heart knowledge) determines right behavior! Workers of iniquity (Scripture twisters) may profess Jesus with their mouths but deny Him by their deeds (see Titus 1:16).
See also How to Test the Spirits.