This Doctor of Ministry thesis-project studies the effect of preaching with the theological emphases of Historic Pietism, with the hypothesis that Pietistic preaching will improve spiritual maturity. The author gave his congregation a pretest congregational health assessment, followed by a six-month experiment period wherein each sermon emphasized a Pietistic theological theme, and then a posttest using the same assessment. Inferring from the comparison of congregational health scores, spiritual maturity improved over the test period. Pietism is a valuable tool for preachers looking to grow their congregation in spiritual maturity.