"Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me."

Paul certainly explained Christianity to us.  But Jesus of Nazareth invented it.  From His first words,  "wist ye not that I must be about my Father's business?" to His last, "It is finished."  He expressed the unshakable belief He Himself was the only begotten son of God, the Son of David, Israel's Messiah.  Read His words - you can't miss it. In every text, Jesus saw Himself, the Holy One of Israel.

There is nothing in Jesus like doubt.  Just sorrow and suffering - and joy at God's choosing.  

You say, "Believing or not has no effect on life..."   You are quoting neither Paul nor Jesus.  You are expressing the antithesis of the Jewish Mind.