The attitude one has toward doing what has to be done determines if the action is legalistic. An illustration makes this clear:

“A serious athlete has to keep training rules. Most athletes are glad to keep them, rigid as they may be, for the sheer love of the sport. A few athletes conform to make the team and glorify, show off, self. The former attitude is love, and the latter is legalism, but both attitudes are toward the same rigid code, and both result in conformity. Having to conform to a law is not of itself legalism” (Charles C. , The Grace of God [Chicago: Moody Press, 1975], p. 7).

Michael P. Green, ed., Illustrations for Biblical Preaching: Over 1500 Sermon Illustrations Arranged by Topic and Indexed Exhaustively, Revised edition of: The expositor’s illustration file. (Grand Rapids: Baker Book House, 1989).

I have just completed a series of lessons on legalism, based on the book of Galatians.  They are available on Amazon in both print and Kindle versions, as well as part of my Good Questions Have Groups Talking Subscription service. For a medium-sized church, lesson subscriptions are only $10 per teacher per year. Lessons correspond with three of Lifeway’s outlines as well as the International Standard Series.