The Gettysburg Address and Bixby letter was a commenoration piece done on the anniversary of Lincoln's birthday. Bixby who lost 5 sons in the war. (My own great grandmother lost 4 sons in WWII)
Large Vintage Bixby letter file box by Hannahandhersisters on Etsy
"Bixby Letter" from Abraham Lincoln. Read in Saving Private Ryan
Using the 'N-gram' technique, researchers from Aston University and the University of Manchester determined famous Bixby letter was 'almost certainly' written by secretary John Hay.