score:3
In evangelism you are right in starting with your friend's conviction and in the process you have successfully identified a major concern: that he is satisfied with little happiness. Your deployment of the cave allegory is thus appropriate but you need to show how staying in the cave is ultimately life threatening.
This is where Platonism differs from Christianity. If we use the original meaning in Platonism (where this allegory originated), it's an allegory for our laziness to stay within the material realm. It's painful to pursue philosophical truths (the sun gets in our eyes), but it's the only way forward for enlightenment. As the allegory was originally conceived, however, it was meant to be optional: to pursue philosophical truths / enlightenment when one is ready, usually at retirement from active life. This meaning is still true for Christians today (especially for those who becomes monk / hermit or who undertakes the path of asceticism & mysticism). But Christianity does NOT require one to pursue this path in order to be saved. In this sense, your friend is right, why bother with hard truths when there are so many visible things to take care and that can bring us earthly happiness (which God declares "good"): family, career, wealth, health?
I understand you try to modify this allegory by making it to mean theological and spiritual truths that are necessary from the young age (cf. Ecclesiastes) so we can be on the safe paths until we arrive in heaven. We all agree (as well as your friend) that these truths that can make us enemies of those who would rather stay in the cave. In other words, you are trying to modify this allegory to mean carrying Jesus's cross to imitate Jesus, which brings us suffering, mockery, and potentially self-chosen denials of some earthly happiness / pursuit.
C.S. Lewis has been instrumental for me to embrace Christianity. He also deploys the allegory of the cave (although not in the way you used it) in his 4th Narnia book, The Silver Chair (see journal article The Silver Chair and Plato's Allegory of the Cave: Archetypes of Spiritual Liberation). The whole Narnia series itself is a gentle allegory to view Christianity from a fresh perspective. But in order for it to be effective, it's necessary to read the whole series, something that may not work for your friend.
Evangelism is a success when the person decides to take up the cross and follow Jesus. At this point your friend seems far from ready, short of God's direct intervention through a crisis, etc. Even Jesus warned us to count the cost.
Therefore, we need to first start by showing the consequences of taking no action:
Then we need to clarify Christianity's position in 2 areas important to your friend (freedom and happiness) and add 2 important elements: morality and new life. This is the general trajectory I find useful:
Platonists, Aristotelians and Stoics teach that:
But common sense, C.S. Lewis, and Christianity disagree with them on both points:
What is the connection between morality and happiness? It is extremely important to note that in Christianity acting virtuously (living a moral life, defined as obeying the voice of conscience planted by God in our nature) does NOT automatically lead to happiness (defined as pleasure and opportunities / resources to experience pleasure). Happiness is a gift (God's reward), which can be experienced starting here, but will only be fulfilled incorruptibly in heaven. Before the world ends, God lets the sun shines on the righteous and the wicked alike, which we can take to mean that God gives happiness in various measures to everyone whether they deserve it or not. Hence the Psalmist's many complaints to God that how come the righteous suffer but the wicked prosper, and the Psalmist's pleas that God should to do something about it soon. So the main salvation question is: how to ensure that God does not take this temporary happiness from us but instead rewards us with eternal happiness in the life to come. The answer: obtain new life (see the next point).
What's the connection between happiness, new life, and morality?
What is the connection between new life and freedom? In Christianity, true freedom has several meanings and some of them are obtained as benefits of having a new life when we become Christian:
The 4 points above are the "key value propositions" important to your friend that Christianity has to offer. The hardest selling point seems to be whether the joy, peace, greater freedom, and promise of ultimate happiness (in the next world) is enough enticement to offset the cost: the promised life of suffering in this world. Even in the best scenario where there is not much external suffering outside the cave, there will be much internal suffering in living a better moral life, because as true Christians we will become more aware of our sins and consequently suffer with remorse and with the hard work to purge those remaining sins within us.
Also, I would make a "full selling disclosure": that happiness in this world is not guaranteed. I was quite shaken when I learned how God took away C.S. Lewis's wife from him despite how C.S. Lewis lived an exemplary Christian life from what I learned through his biographies and letters (see the beautifully made movie Shadowland (1993) despite two major inaccuracies). This underscores my conviction that happiness is a gift, not a right obtained through moral living pleasing to God.
The movie shows 3 Christian truths of life outside the cave that are hard to swallow although they lead to imperfect happiness now and heaven in the future:
“I love you, Joy. I love you so much. You made me so happy. I didn't know I could be so happy.”
“Twice in that life I've been given the choice: as a boy and as a man. The boy chose safety, the man chooses suffering. The pain now is part of the happiness then. That's the deal.”
“I suggest to you that it is because God loves us that he gives us the gift of suffering. Pain is God's megaphone to rouse a deaf world. You see, we are like blocks of stone out of which the Sculptor carves the forms of men. The blows of his chisel, which hurt us so much are what make us perfect.”
Once your friend believes that becoming Christian is the only way to obtain new life, the last step is for your friend to take action. Otherwise you'll need to take additional apologetics steps by showing the trustworthiness of the Bible, how prophecies were fulfilled in Jesus, etc.