Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
Beloved - the affectionate address wherewith he calls attention to an important subject.
Every spirit - in the person of a prophet. The Spirit of truth, and that of error, speak by men's spirits as their organs. There is but one Spirit of truth, and one of Antichrist.
Try - by the tests (1 John 4:2-3). All are to do so: not merely ecclesiastics. Even an angel's message should be tested by the Word of God; much more men's teachings, however holy the teachers seem (Galatians 1:8).
Because ... - reason why we must test the spirits.
Many false prophets - not in the sense 'foretellers,' but organs of the spirit that inspires them, teaching error: 'many Antichrists.'
Are gone out - as if from God.
Into the world - said alike of good and bad prophets (2 John 1:7). The world is easily seduced (1 John 4:4-5).