Because John loves the church, he gives this strong warning. Those who think that a ministry of warning is unloving have set their love on something other than the truth of God and on the church of God.
Those who treat false prophets as a thing of the past have not taken account of the word ‘many’. Many false prophets have gone and continue to go out into the world in every age, so that churches can never cease to be vigilant and every generation needs to be alert to the new forms which error takes. John’s epistle is given to fight all of them, not just the ones of his own day.
Who are the false prophets in our own day? Obviously they include the cults and those who promote liberal theology, but they also include the Prosperity Gospel teachers, and those who pose as Evangelicals, but who have abandoned a distinctive and holy Christian life.
Why speak of false prophets and not of false teachers? Prophets belong only to the foundation stage of the church before the New Testament was complete, while teachers are found throughout the entire age. However false prophets have continued long after New Testament times, and will trouble the churches to the very end; they claim to speak direct from God. Nevertheless all false teachers are also covered by this verse.