Gary Thomas emphasizes that the primary purpose of marriage is to make us holy, not just happy. He argues that through the challenges and joys of marriage, couples can grow in their spiritual lives and develop a deeper relationship with God. This perspective shifts the focus from personal satisfaction to spiritual growth, making marriage a powerful tool for character formation and spiritual discipline.

"Sacred Marriage" provides practical advice on how to turn marital struggles into opportunities for spiritual and personal growth. Thomas encourages couples to confront their weaknesses and sins, using these challenges as a means to grow closer to God and each other. By viewing struggles as a chance to develop patience, forgiveness, and love, couples can strengthen their relationship and their faith.

The book highlights the importance of spouses supporting each other in their spiritual journeys. Thomas discusses how couples can partner in prayer, worship, and service, helping each other to grow in their faith and character. This mutual support not only enhances the spiritual lives of both partners but also deepens their bond and creates a more meaningful and fulfilling marriage.