In the Gospel, Jesus leaves home and starts preaching and developing a following. In the First Letter of John we are challenged to test the voices we hear and to place Jesus' message above all others. Ask yourself, why do you believe in Jesus?
Based on 1 John 3:22-4:6:
We receive from God whatever we ask, because we obey his commandments and do what pleases him. And this is his commandment, that we should believe in the name of his Son Jesus Christ and love one another, just as he has commanded us. All who obey his commandments abide in him, and he abides in them. And by this we know that he abides in us, by the Spirit that he has given us.
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. And this is the spirit of the antichrist, of which you have heard that it is coming; and now it is already in the world. Little children, you are from God, and have conquered them; for the one who is in you is greater than the one who is in the world. They are from the world; therefore what they say is from the world, and the world listens to them. We are from God. Whoever knows God listens to us, and whoever is not from God does not listen to us. From this we know the spirit of truth and the spirit of error.
(New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org)