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"I have recently been examining all the known superstitions of the world, and do not find in our particular superstition (Christianity) one redeeming feature. They are all alike founded on fables and mythology." - THOMAS JEFFERSON

Understanding religious delusion -
Let's imagine that I tell you the following story:

There is a man who lives at the North Pole.
He lives there with his wife and a bunch of elves.
During the year, he and the elves build toys.
Then, on Christmas Eve, he loads up a sack with all the toys.
He puts the sack in his sleigh.
He hitches up eight (or possibly nine) flying reindeer.
He then flies from house to house, landing on the rooftops of each one.
He gets out with his sack and climbs down the chimney.
He leaves toys for the children of the household.
He climbs back up the chimney, gets back in his sleigh, and flies to the next house.
He does this all around the world in one night.
Then he flies back to the North Pole to repeat the cycle next year.
This, of course, is the story of Santa Claus.
But let's say that I am an adult, and I am your friend, and I reveal to you that I believe that this story is true. I believe it with all my heart. And I try to talk about it with you and convert you to believe it as I do.

What would you think of me? You would think that I am delusional, and rightly so.

Why do you think that I am delusional? It is because you know that Santa is imaginary. The story is a total fairy tale. No matter how much I talk to you about Santa, you are not going to believe that Santa is real. Flying reindeer, for example, are make-believe. The dictionary defines delusion as, "A false belief strongly held in spite of invalidating evidence." That definition fits perfectly.

Since you are my friend, you might try to help me realize that my belief in Santa is a delusion. The way that you would try to do that is by asking me some questions. For example, you might say to me:

"But how can the sleigh carry enough toys for everyone in the world?" I say to you that the sleigh is magical. It has the ability to do this intrinsically.
"How does Santa get into houses and apartments that don't have chimneys?" I say that Santa can make chimneys appear, as shown to all of us in the movie The Santa Clause.
"How does Santa get down the chimney if there's a fire in the fireplace?" I say that Santa has a special flame-resistant suit, and it cleans itself too.
"Why doesn't the security system detect Santa?" Santa is invisible to security systems.
"How can Santa travel fast enough to visit every child in one night?" Santa is timeless.
"How can Santa know whether every child has been bad or good?" Santa is omniscient.
"Why are the toys distributed so unevenly? Why does Santa deliver more toys to rich kids, even if they are bad, than he ever gives to poor kids?" There is no way for us to understand the mysteries of Santa because we are mere mortals, but Santa has his reasons. For example, perhaps poor children would be unable to handle a flood of expensive electronic toys. How would they afford the batteries? So Santa spares them this burden.
These are all quite logical questions that you have asked. I have answered all of them for you. I am wondering why you can't see what I see, and you are wondering how I can be so insane.
Why didn't my answers satisfy you? Why do you still know that I am delusional? It is because my answers have done nothing but confirm your assessment. My answers are ridiculous. In order to answer your questions, I invented, completely out of thin air, a magical sleigh, a magical self-cleaning suit, magical chimneys, "timelessness" and magical invisibility. You don't believe my answers because you know that I am making this stuff up. The invalidating evidence is voluminous.