Great Mystery

What is the “great mystery” Paul identifies in Ephesians 5:32? Is it the relation of Christ and His church? The connection between Christ-church and man-wife?

In context, one particular dimension of Paul’s teaching is perhaps especially in view. Verse 31 quotes from Gen 2:24, and most immediately the mystery is the application of Gen 2:24 to Christ and the church. That is, the mystery is that Christ has left His Father to cleave to His wife and become one flesh with her. The mystery is incarnation for the sake of union with the bride.

(This interpretation, of course, is weakened by the fact that verse 31 names “father and mother” – did the Son leave a mother?)