See prof Robert Yarbrough lectures on Schlatter: https://www.covenantseminary.edu/resources/the-francis-schaeffer-lecture-series-1995-fall-adolf-schlatter-the-future-of-christianity/
For more on John Piper and Adolf Schlatter, see: https://www.desiringgod.org/articles/not-smoking-could-even-give-us-an-edge-on-schlatter