Well, that’s just the thing Marco. While it is based on both faith and reason, and reason can take you as far as the historicity, and I believe even the divinity of Christ, (if one is predisposed to divinity at ALL). Once you can see that Christ is Lord, however you get there, then you can trust the scriptures as authoritative, and can accept them on their face, without the stumbling block of logic formulas. The Lord, would by necessity be truth, and could only convey truth. So at this point, one can read the narratives of the atonement and garner an innate understanding of what is going on here. You’re not looking to trip up the evangelists who are writing the scripture. You’re looking at them through the eyes of belief, which in the end, is a grace of God. Hence the old expression:
For a believer, no explanation is necessary. For a non believer, no explanation will suffice, (or something to that effect.)
And so, we believers can only try to lead the nonbeliever to a disposition of openness to the truth. The Holy Spirit must to the rest. It’s humbling to know that I will in fact not likely be the agent that the Holy Spirit chooses to bring some of my friends and loved ones to God. But on the other hand, He did allow me to be the agent for some. For the others, I only pray that the Holy Spirit will act in their lives, and that they will be granted the grace of faith. This may seem small, but since faith is ultimately a grace of God, it is the largest task which we are given.
So what am I saying here? Good question. I think what I’m saying is that we do our best to help someone consider Jesus Christ in a fuller light, and to come to trust that He is who He said He is, and then, having planted that seed, water it with prayer and fasting. The Lord Himself will do the rest.