“Standing in a garage no more makes you a car than standing in a church makes you a Christian.”

in Press, Radio, Television, Periodicals, Public Relations, and Advertising, As Seen through Institutes and Special Occasions of the Henry W. Grady School of Journalism (1967) edited by John Eldridge Drewry.

Though Keillor has been quoted on the internet and in print as having made this or a similar remark, such expressions have been made by others, and may have originated with Billy Sunday, who is quoted as having said "Going to church on Sunday does not make you a Christian any more than going into a garage makes you an automobile!" in Press, Radio, Television, Periodicals, Public Relations, and Advertising, As Seen through Institutes and Special Occasions of the Henry W. Grady School of Journalism (1967) edited by John Eldridge Drewry.
Disputed
Variant: Going to church no more makes you a Christian than standing in a garage makes you a car.

Source: Roger Biles, The human tradition in urban America http://books.google.pl/books?id=DqayY98DDDcC&pg=PA128&lpg=PA128&dq=church+garage+automobile&source=bl&ots=NMnjn43sFY&sig=I-YoAzHs5ChdCEE6lsOEK073WQY&hl=pl&sa=X&ei=sUsCT6-QE8vJsgb4qfmDAg&ved=0CCUQ6AEwAQ#v=onepage&q=church%20garage%20automobile&f=false (2002), p. 128.

Source: Rules for Radicals: A Practical Primer for Realistic Radicals (1971), p. 128

Ron English's Fauxlosophy: Volume 2 (2022)

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 145.

Source: The Final Warning