The purpose of this quantitative, non-experimental study was to assess the effects of adult learning principles (ALP) in sermons on parishioners' spiritual growth. Sermons have been central to the spread of Christianity. Given the significant role sermons play in parishioners' spiritual formation and growth, examining sermons' effectiveness is crucial. One-hundred-and-twenty participants responded to the researcher-created research instrument. An initial screening was first conducted with the study's data; as a result, 13 participants were removed from the data set for complete non-response to the 15 survey items. Three research questions and hypotheses were formally stated to address the study's topic. Over 95% of study participants agreed with the statement that their pastor's sermons contribute positively to their spiritual formation. No significant difference in perception was found between university students and church members that their pastor's use of adult learning principles had contributed positively to their spiritual growth. All 15 learning principles represented in the survey items reflected statistically significant mathematical relationships. Three principles (content, language, and scenarios) surfaced that reflected very strong to huge relationships with study participants' perceptions that their pastors' sermons positively impacted their spiritual formation. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]