For whatsoever is born of God overcometh the world: and this is the victory that overcometh the world, (even) our faith. Who is he that overcometh the world, but he that believeth that Jesus is the Son of God?

If the love of God dwells in the heart of the child [the one who has their faith in God, and has been born again] of God it must be manifested in a practical way. Love must be expressed in deed and in truth, which is the fruit of true faith. If the believer does this he or she knows that they are of the truth. If it is lacking he is but an empty professing believer. But if we know that we are of the truth, by bearing such fruit of faith, we can assure our hearts before Him, and we can draw nigh with confidence.