What does To one who has faith , no explanation is necessary. To one without faith, no explanation is possible." mean?

Explanation:

Take some of the hard to explain passages in the Bible (or some contradictions).

Those who have faith don't need to know what the passage means at all. They accept what is part of their faith as all that matters. If they don't understand something, they believe that if they leave it alone or pray about, eventually the meaning will become clear. And if it never does, then God will reveal it perhaps after death. It doesn't matter.

To someone without faith, the meaning will never be clear even if one is offered. They can't accept it because their understanding will not permit them to care about whatever it is that seems unclear. To them it does not matter because the premise that religion is built on is false. No answer can bridge that gap.

I hope I'm being fair to both sides. I have faith so if you get a better answer from those who do not, then their explanation is the one you should accept.

because their parents smoke while in labor