In this sermon, the preacher emphasizes the importance of spiritual reality and the need for believers to actively cooperate with the Holy Spirit. He explains that spiritual reality is not necessarily something spectacular, but rather a daily process of being led by the Spirit of Truth. The preacher highlights the role of discipline in this process, both through external circumstances and internal revelation. He encourages believers to surrender themselves to God and allow the cross to expose and cut off anything that is not real or of the old creation. The ultimate source of spiritual reality is found in God, specifically in Jesus Christ who became incarnate to make reality available to all believers. The preacher concludes by urging listeners to seek spiritual reality and not settle for deception or mere appearance.