There are three steps there, two that are rational and one that relates to faith.
The first is that Theism makes more sense and is more rational than atheism. I believe that any person can come to that conclusion with different degrees of clarity, from a perception of a generic "divine stuff" to the more precise "God of Philosophers", in Aristotelian forms.
That would leave us with a generic divinity, not to the Triune Christian God. That is hinted in the Old Testament, but it's really a revelation we get from the life of Jesus Christ. The second rational step, then, is that there is enough historical evidence for the fact that Jesus Christ existed, that the main miracles ocurred and that He was crucified and resurrected in flesh, in history. One can learn that and still not believe, just be aware of a sheer fact.
Now, the third step is faith, trust. Faith points toward invisible things, but starts with visible ones. If this man did what He did, if He truly died and resurrected this is very serious. Enthropy itself was reversed, or, in cultural terms, death was destroyed, if the conscience that emerged on the third day is the same conscience that died on Friday, it means that it was kept above and beyond every natural law. Only that one First Cause could do that and in doing it we are revealed things we could not have assumed: it's personal, it became completely human without ceasing to be completely God. And if this God and He tells us about a Father and a Holy Spirit that we can't see, we knowing the visible Human-God, trust Him on that which we can't see. That's faith. When He promises that bread and wine *will* be His body and blood, we trust Him because of Whom we saw. When He says that there will be *one* community that will be His unbroken body, we trust Him (at least some of us do).