"For no one ever hated his own flesh, but nourishes and cherishes it, just as Christ does the church, because we are members of his body. 'Therefore a man shall leave his father and mother and hold fast to his wife, and the two shall become one flesh.' This mystery is profound."
Eph 5:29–32
When the Apostle Paul likened the marriage relationship to Christ and His church in Ephesians 5:22-33, he wrote this in vs. 32 "this mystery is profound." The word profound here in the original language is "mega." When God's word attaches "mega" to something, it means in the heart of God it is a great thing.
The first great thing about this mystery revealed to us is that of intimacy. In a similar way that marriage can be the most intimate relationship between two people on earth, so is that relationship between God and His people. Through Christ God has revealed to us His intent to redeem and reconcile a people unto Himself that we would relate personally and intimately with Him. This indeed is a great thing!
Another aspect of this greatness concerning marriage and Christ and His church is that of oneness and unity. In vs. 31, Paul quotes from Genesis 2:24 concerning marriage, "the two shall become one flesh." There is the great potential for oneness here within the marriage relationship. When a wife and a husband are relating to each other in love and godliness there will be an absence of conflict and an abundance or greatness of unity. When God's people are following Jesus, there will also be oneness with Jesus in terms of our will, our thoughts, and actions.
This is partially the idea of Matthew 11:30-31 when Jesus invited us, "Come to me you who are weary and heavy laden and I will give you rest, take my yoke upon you." The idea of a yoke in the ancient world describes two oxen working together as one. When yoked to plow a field, one ox cannot left, while the other goes right. In a similar way when we are yoked with Jesus, we will be one with Him.
There is one more aspect of the greatness in this mystery revealed and that is service. Christ came "not to be served but to serve and give His life as a ransom for many." (Matt 20:28) In a similar way, husbands are invited to sacrificially love their wives by "giving themselves up for her." Wives are invited to "submit to their husbands," as Christ submitted to the Father. The idea here of service is putting the interests of the other first.
We shouldn't be surprised how mystified the disciples were in John 13, when Jesus stripped down to his undergarments and began washing their feet. Peter recoiled at this gesture and no doubt the other disciples were confused. But Jesus was demonstrating a principle that God's people are to follow in their marriages, churches and communities, "If I then, your Lord and Teacher, have washed your feet, you also ought to wash one another’s feet... If you know these things, blessed are you if you do them." (vs. 13-17)