Yesterday, Pastor Joelle posted something really, truly important on her blog. You should read it.
Basically, she challenges the Bonhoefferian cliche "cheap grace." Billige Gnade. Whether or not Bonhoeffer intended it, which is a question for experts, the expression is often used as a back-door return to legalism. Typically, it goes like this. You say, "Salvation is a free gift of God to all people," and then somebody else says "As long as we [confess our sins] [have a personal relationship with Jesus] [recognize the Pope as Christ's vicar on earth] [eat Wheaties]."
And when, as Pastor Joelle points out, you say, "Actually, 'free' means 'free,'" then your interlocutor suggests that you go read The Cost of Discipleship. Again.
Anyway, she's onto something big here. Read her post.