“The difference between a rut and a grave is the depth” is a saying that has been printed on many posters. Brooklyn clergyman S, Parkes Cadman (1864-1936) said in 1902:
 
“He (Cadman—ed.) warned Sunday-school teachers to keep out of ruts for the only difference between a rut and a grave is a matter of depth.”
 
American novelist Ellen Glasgow is often credited with the saying, but there is no evidence that she said it before the 1920s. “THE ONLY difference between a rut and a grave is in their dimensions.—Ellen Glasgow” was printed in The Reader’s Digest in 1936.
 
Gerald F. Burrill (1906-2001), the eighth Bishop of Chicago in The Episcopal Church, is also often credited with the saying, but he most probably used it later than both Cadman and Glasgow.
 
   
Wikipedia: S. Parkes Cadman
Samuel Parkes Cadman (December 18, 1864 – July 12, 1936), better known as S. Parkes Cadman, was an England-born American clergyman, newspaper writer, and pioneer Christian radio broadcaster of the 1920s and 1930s. He was an early advocate of ecumenism and an outspoken opponent of anti-Semitism and racial intolerance. By the time of his death in 1936, he was called “the foremost minister of Congregational faith” by the New York Times.
(...)
Rev. Cadman was buried in Brooklyn, New York, where he is memorialized in Cadman Plaza, named in his honor by New York City in 1939. The Central Congregational Church in Brooklyn was renamed Cadman Memorial Church in 1942 in his memory.
 
Wikipedia: Ellen Glasgow
Ellen Anderson Gholson Glasgow (April 22, 1873 – November 21, 1945) was an American novelist who portrayed the changing world of the contemporary south.
 
Wikipedia: Gerald F. Burrill
The Rt. Rev. Gerald Francis “Frank” Burrill (June 8, 1906 - July 17, 2001) was the eighth Bishop of Chicago in The Episcopal Church.
         
29 November 1902, Bridgeton (NJ) Evening News, “State Sunday-School Workers: A Review of Their Recent Convention,” pg. 3, col. 2:
He warned Sunday-school teachers to keep out of ruts for the only difference between a rut and a grave is a matter of depth.
(Rev. S. Parkes Cadman, D. D., of New York.—ed.)
 
Chronicling America
26 June 1905, Evening Bulletin (Honolulu, HI), pg. 1, right masthead:
Notice to merchants who do not advertise:
The only difference between a rut and a grave is the length and breadth.
 
Old Fulton NY Post Cards
16 January 1915, The New York Clipper, pg. 16, col. 3:
JOHN B. WARREN SAYS:
“The difference between a RUT and a GRAVE is simply a matter of inches and an undertaker.”
Some philosophy, that.
 
Google News Archive
25 September 1915, Deseret Evening News (Salt Lake City, UT), pg. 9, col. 1 ad:
The Only Difference Between a Rut and a Grave Is The Length and the Breadth.
(“Utah’s fine coals—Castle Gate and Clear Creek.”—ed.)
   
Google Books
The Lyre of Alpha Chi Omega
Volume 31, Issue 1
1927
Pg. 54:
Now Ellen Glasgow tells us that the only difference between a rut and a grave is in their dimensions.
 
Google Books
The Reader’s Digest
Volume 28
1936
Pg. 15:
THE ONLY difference between a rut and a grave is in their dimensions.—Ellen Glasgow
 
Google Books
How to Win and Hold a Husband
By Elizabeth M. Gilmer
New York, NY: Arno Press
1974 [©1939]     
Pg. 159:
They are married to women who have let marriage get into a rut and, as somebody has pithily said, the only difference between a rut and a grave is the depth.
 
Google Books
And I Quote:
The Definitive Collection of Quotes, Sayings, and Jokes for the Contemporary Speechmaker
By Ashton Applewhite, William R. Evans III and Andrew Frothingham
New York, NY: St. Martin’s Press
1992
Pg. 252:
The difference between a rut and a grave is the depth. — Bishop Gerald Burrill
 
Google Books
Power Stars to Light the Business Flame:
The Visionaries and You
By Hank Moore
Houston, TX: Di Angelo Publications
2012
P. ?:
“The difference between a rut and a grave is the depth.” Gerald Burrill