" The people of that time had what they called “mystery religions.” These religions offered special secrets only to those who passed through a closely guarded process of initiation. Unless you had been initiated, you could not learn their secrets. When Paul describes marriage as a “mystery,” therefore, he implies that we can understand its true nature only if we have passed through the appropriate process of initiation. This process takes place when, by the marriage ceremony, a man and woman enter into covenant with God and with each other. Only when they are willing to make this covenant commitment can they begin to discover the true nature of marriage. Couples not willing to fulfill this condition can experience the legal and physical aspects of marriage, but its true nature remains closed to them. It is still a mystery—a secret. "

― Derek Prince , Husbands and Fathers: Rediscover the Creator's Purpose for Men