He could mention the moral arguments... but each man of conscience can recognize these also, outside any religious belief.
He could maybe unfold some modern scientific arguments which indeed, point to the existence of an intelligent and incredibly careful creator... but the nonbeliever may easily observe that none of them implies that this mysterious creator incarnated himself as a man in order to bring the example of divine love to mankind and ensure its salvation.
He could enumerate the prophecies of the Old Testament, also confirmed by the ancient Dead Sea Scrolls, which find their fulfillment in the life of Jesus, as it is described in Gospels. However, these ones will usually not attract the unbeliever, for he already heard other theories which seem to demonstrate irrefutably the fallacies and contradictions of the Scriptures.
He could then mention the New Revelation through Lorber and Mayerhofer, which confirms the Scriptures and credibly answers to all attacks against it. Unfortunately, it seems that very few would take some interest in studying a very large teaching which has absolutely no official recognition in the world. In other words... even if reading from the New Revelation, would bring something interesting to them, they would rather chose to stay on the "safe side" of skepticism, because no worldly authority supports this teaching.
Finally... the believer may then simply affirm that to be a true Christian means not only to love your fellowman, but also to be able to keep this love alive against all enmities and injustices, to be able to turn your self-love, resentments and hate into love, by means of forgiveness and compassion. He may conclude that to be a true Christian means to be an apostle of unconditional, invincible, supreme love.
Some proof for this?... Any seeker may browse the old and modern history of Christianity and discover at every step believers letting themselves killed on the cross, given to the lions, chopped off, tortured and killed in an unimaginable variety of ways, for their faith.
Could just some mental delusion lead to such incredible sacrifices? Certainly, not.
Could a great love and a great promise of love lead to them? Certainly, yes. And real faith is nothing else but the living promise of love.
In a world in which love is the most misunderstood and betrayed thing, the Christian martyrs represent in the purest way the fundamental truth any good parent and true lover recognizes: life is less than love.
So, finally, coming back to our question... why should an unbeliever be interested in becoming a Christian?
Well, simply because he might get to be interested in discovering the love which is, at all times, greater than life.
Opinions and Testimonies
of believers in the New Revelation as the Lord's direct Word