The sermon centers on the necessity of spiritual purity and discernment in partaking of the Lord's Supper, using the metaphor of 'leaven' to warn against hidden, small sins that corrupt the church's unity and holiness. Drawing from 1 Corinthians 11, it emphasizes that the Lord's Supper is not a casual gathering but a sacred act requiring self-examination, unity of faith, and the removal of hypocrisy, malice, and division—symbolized by the unleavened bread of the Passover. Pastor Friesen calls for a return to biblical standards, rejecting open communion and worldly influences, urging believers to examine their hearts for hidden sins, false doctrines, and double lives, and to live with sincerity and truth, reflecting the true body of Christ in both doctrine and conduct.