To one who has faith, no explanation is necessary.

That sounds laudable, so lets look at some history:

When I was four years old, I had faith, faith that Santa would be at my house on Christmas eve. But, I had more than faith, I had EVIDENCE. Mom and dad assured me that Santa was coming. I sat on his lap at Macy's. I left cookies and milk for him on Christmas eve. The milk was partially gone and there was a bite out of one of the cookies I left for him. And the gifts. Who can forget the presents. As most of you know, that was all a ruse, a conspiracy by mom, dad, Macy's, Hasbro, Mattel and many others. They all lied to me. I had faith, but I was deceived.

Then, a couple of years later, my faith was tested when I lost a tooth. Again, I had more than faith, I had evidence. At the insistence of mom and dad, I put the tooth under my pillow. Low and behold, there was a money there in the morning. I continued to have faith for another four teeth until I learned the truth. Again, I had faith, but I discovered I was decieved.

So if you have faith of God's existance, how do you know you are not being decieved. After all, everything you know about Yahweh you were told by another party, a party who could be deceiving you in their own self interest, be it power, control, money, or their own desperate hope of Heaven.

As for St. Thomas Aquinas, I quote Matt Dillahunty. or another of his quotes,