Though Christians commonly think we need to move beyond having doctrinal differences, John informs us that this is an impossible task.  We are in the last hour (2:18), so we need to constantly test those that come to us, claiming to teach God's word.  Though Satan is mortally wounded, he is still a great danger; the spirit of Antichrist is found in deceitful spirits, who are empowering false prophets.  Our calling is to test a teacher's message concerning Christ (4:2-3) - do they articulate the true gospel?  Second, we are called to examine whether a teacher is committed to the Apostles' teaching - are they listening to the Apostles' message, which is recorded in Scripture, or are they trying to supplement or even detract from it?