"This quote from Thomas Boston is taken from an old magazine article in the author's files. Unfortunately, neither the title of the magazine nor the date of publication was listed on the clipping." (Op. cit., footnote 3, pg. 157)
The original source for this quote in the works of Thomas Boston is:
An Illustration of the doctrines of the Christian Religion: with respect to with respect to both Faith and Practice, upon the plan of the Assembly's Shorter Catechism, comprehending A Complete Body of Divinity, 3 vols., (Edinburgh: John Reid, 1773), III:94-95.
This work is available as a free download (public domain) from Google books at:
Here is the way the quote appears in the original:
"They that would keep themselves pure must have their bodies in subjection, and that may require in some cases a holy violence, I Cor. ix. 27."
Just to keep the record straight!
P.S. I did contact Jerry Bridges about this via email on May 9, 2010. His response on May 10, 2010 follows:
"Thanks so much for this information. I doubt that NavPress will be
interested in changing the footnote at this late date, but I will bring this to their attention."