I recommend this article that bring more things to the light of truth- UNDERSTANDING THE BASICS OF PIETISM by Apprising Ministries

Excerpts:
Luther argued that vowing something that God had not commanded is sinful: “The very foundation of the monastic vows is godlessness, blasphemy, sacrilege, which has befallen them because they spurn Christ, their leader and light, and presume to follow other things they think better.”

“…Today the largest new pietist movement is the Emergent Church…”

“Furthermore, the Purpose Driven movement is also a pietistic movement. Rick Warren claims there are world class Christians that are in a better category than ordinary Christians. He had his followers take a long oath at a baseball field to pledge themselves to serving his new reformation.”