“Mr. Lincoln’s religion is too well known to me to allow of even a shadow of a doubt; he is or was a Theist & a Rationalist, denying all extraordinary — supernatural inspiration or revelation,” Herndon wrote in the letter, signed Feb. 4, 1866, a year after Lincoln’s assassination.

“At one time in his life, to say the least, he was an elevated Pantheist, doubting the immortality of the soul as the Christian world understands that term,” continued the letter, addressed to Edward McPherson, Clerk of the U.S. House of Representatives. “I love Mr. Lincoln dearly, almost worship him, but that can’t blind me. He’s the purest politician I ever saw, and the justest man.”