I found this is the book I'm read called Money, Possessions, and Eternity by Randy Alcorn. He's speaking in the context of tithing, specifically excuses people might make not to tithe. But what he says is so well put and important, I just had to post it. :)
Excuse: "Tithing is legalistic."
Response: "Any legitimate practice can be done with a legalistic attitude. The fault is with the heart, not tithing itself. What I have noticed, however, is that some people call anything "legalism" that sets a responsiblity upon them or requires discipline from them. If any principle gets too close to home, starts meddling in my life, requires sacrifice or commitment on my part, then I can dismiss it simply by calling it "legalistic". Hence, legalism easily becomes a convenient label to cover up my own unwillingness to obey God."
