“Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world. By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, and every spirit that does not confess Jesus is not from God.” – 1 John 4:1-3 (ESV)
The mention of the Holy Spirit in the previous chapter (1 John 3:24) motivates John to advise his readers that other spirits exist, such as demonic spirits, who produce false prophets and false teachers to spread their false doctrine. We are warned repeatedly through Scripture of the danger of apostasy, especially in later times. (1 Timothy 4:1-2). We are in later times as it is the period from the first coming of Christ until His return for his Church and judgment of the world. Do be on guard against falling prey to false teaching that tickles our ears and stirs our desire for the things of the world. Our promise is this, we can know and do know the Holy Spirit of God if we by faith given to us have believed in Jesus and His sacrifice on our behalf. We just might be in a time where the opposition is increasing and it is wise for us to cling to this instruction. We can test the spirits by discerning whether they confess Jesus as Lord and Savior. Those who do not so confess, but pretend to be preachers and teachers, are apostate.