Bible Verses About Warfare of Saints: The world

these things I have spoken to you, that in me ye may have peace, in the world ye shall have tribulation, but take courage--I have overcome the world.'

because every one who is begotten of God doth overcome the world, and this is the victory that did overcome the world--our faith;

who is he who is overcoming the world, if not he who is believing that Jesus is the Son of God?