For this cause shall a man leave his father and mother, and shall be joined unto his wife, and they two shall be one flesh.
Just like we have left the old man and have become part of Christ's body, so ought the man leave his father and mother and join himself as one to the wife.
An interesting thought: Jesus Christ left His Father, to come to earth so that He might provide all things for the body, that He might make a way to sanctify and cleanse her. Christ could have stayed in heaven with His Father to provide all of this, but instead, He chose to take the discomforts of life. Perhaps this is more of an example of how the husband ought to "leave and cleave." Christ left His Father, but still communed with Him. So the man ought to leave his parents, but not cease communing with them. Christ gave His all for His bride. So the man ought to give his all for his bride. Christ provided all that He could for the spiritual nourishment of His bride. So the man ought to provide all that he can for spiritual nourishment.
Nevertheless let every one of you in particular so love his wife even as himself; and the wife see that she reverence her husband.
Even though we won't be able to fully understand it, the husband and wife are given instructions and rules to help them (husbands: love, wives: reverence). We don't have to fully understand the relationship between Christ and the church to follow what He has shown us; that in itself will be lessons enough for a lifetime of marriage.