The wedding season is upon us and with it a renewed interest in this most fascinating ceremony of Jewish life - marriage.
During the last wedding I attended, the mother of the groom mentioned the well known phrase from Genesis, chapter 2, verse 24: "Therefore shall a man leave his father and his mother, and shall cleave unto his wife, and they shall be one flesh."
This is a most beautiful verse. I've heard it before and it always struck me as profound in some way, but this time it really got me thinking – what does it mean to leave the parents? Has this been addressed in the past? Is the intent merely physical or also spiritual, and if so, in what manner?
If you are interested in food for thought while you're standing around waiting for the ceremony to begin (average delay: 1 hour, Israeli time), as well an idea or two for a wedding present, here's my two bits:

The Halacha Interpretation
Well, I am definitely no Halacha expert, but I do have a copy of the popular Da'at Mikra and from it I learn that Rashi took this verse to mean a physical separation so as to prevent incest. The writers of Da'at Mikra also says that the meaning is physical, intended to reduce the fighting that may occur for instance, between the bride and her mother in law. In any case, they say, this is not actually a mitzvah but rather just the natural order of things. An internet search for this phrase in Hebrew or English yields an astoundingly small number of results, none of which were actually relevant to my question. I would be glad to hear of any other Halacha-acceptable interpretations from my readers but until then, I will try to give my own interpretation which will be, as usual, from the inside:

The Parent As a Psychological Function
It is possible to interpret this verse from a psychological viewpoint if we understand the parent as representing not only a physical presence but also a psychological function. This function has been described by Transaction Analysis:

The Parent:

This is our ingrained voice of authority, absorbed conditioning, learning and attitudes from when we were young. We were conditioned by our real parents, teachers, older people, next door neighbors, aunts and uncles, Father Christmas and Jack Frost. Our Parent is made up of a huge number of hidden and overt recorded playbacks. Typically embodied by phrases and attitudes starting with 'how to', 'under no circumstances', 'always' and 'never forget', 'don't lie, cheat, steal', etc, etc. Our parent is formed by external events and influences upon us as we grow through early childhood. We can change it, but this is easier said than done."

In short the Parent, with a capital "P" is our code of behavior, some of it conscious most of it not. It is behind many of our quick involuntary social reactions, our likes and dislikes and our prejudices. It is everything we received, for better and for worse from the authority figures in our lives, and also-everything we did not receive- meaning any gaps in our information about the world. Such gaps may vary from sexual misinformation to spiritual neglect.
Transactional analysis was invented by Eric Berne, a psychologist who became disillusioned with Freudian practice and thought he could a formulate a more accurate and more easily understood psychology (needless to say, he was ostracized by the psychological community). The most popular presentation of his theory was written by his colleague Thomas Harris in the bestselling "I'm O.K you're O.K."

In any case – we now have our psychological Parent, and we can now rephrase the original verse thus: Therefore shall a man leave his Parent, and shall cleave unto his wife, and they shall be one flesh."
If this is true, why is it so important to leave the Parent before marriage? What happens if you don't? Is this the man's duty alone? Should the man leave his Parent and the women retain hers?
The answer to these questions lie, I believe in the second part of the verse, which defines the goal of the marriage: "to be one flesh"

"To Be One Flesh"
This can be taken to mean a simple physical union, creating a newborn child which unites the married couple in "one flesh" as Rashi comments. Da'at Mikra says that they shall treat one another as if they were one flesh, meaning they will complete each other – spiritually - until they feel they are as one.
But if the bible is talking about a psychological union between two people then we must ask how can this be possible? In other words, how can two people retain their unique individuality, and yet, at the same time be as one? I see two possibilities.

The Symbiotic Union
In this marriage the couple unite unconsciously. Most of what they think and feel about each other and themselves remains unknown to them. They react to each intuitively, for better or for worse. They are driven by inner forces, including the Parent, to love or hate each other, to remain committed, or to divorce, to talk about the difficulties, or ignore them, or blame each other in an endless, hopeless cycle of unconscious irresponsibility.
Most marriages assume this state of affairs rather quickly. Sometimes the couple are satisfied with it and remain married for years, but increasingly often, this does not suffice. Marriage holds a great promise of "becoming one flesh" and many more people than ever before are unwilling to settle for less, which is why divorce rates are skyrocketing.
But there is another possibility waiting for every new couple to realize.

The Conscious Marriage
In this marriage the couple make a conscious effort to understand themselves. All the unconscious parts of the psyche are brought to light in a long and painful but exciting and hopeful process.
A major component of this process is checking each and every component of the Parent: every judgmental remark or attitude, whether positive or not must be brought into the light and it's contents examined. For example, the husband may be bothered by the incessant chattering of his wife (which he found delightful before they got married) while his wife may be depressed by her husbands long silences (which she found intriguing and full of promise before they got married). Such feelings and thoughts are brought into the open and examined.
Only when the Parent has been banished from the psyche, can a true spiritual union between two independent individuals become a feasible possibility.
When this happens it will become clear that the partners do indeed compliment each other beautifully. Traits that the man has been missing are possessed by his wife and vice-versa. The husband will understand why he does not talk, and his wife will know why it scares her so much, and they both will learn the opposite – the man will start talking, and love it, and the wife will cherish her new-found ability to enjoy silence, her own and others.
In this manner both become complete, whole individuals. The relationship becomes one of independence not dependence. If a man can cook for himself, iron his shirts, and clean the house he is not dependent on his wife to do so. He can love her for what she is, not for the services he needs to receive from her. When a woman is financially independent, she will be freer to be honest about her feelings towards her husband and decide if she loves him for what he is, or she is sticking around because she was taught that women aren't supposed to work

Conclusion: Married Couples Must Choose Between God or Their Parents
In researching this article I came across what seems to be a well-known commentary:

Rabbi Joshua ben Korha said that man at first was called Adam to indicate his natural constitution--flesh and blood (dam). But when woman was created, the two were referred to as fiery (esh)--living, dynamic beings. God insinuated Himself into the marriage, then added two letters of his own name, Y and H, to the names of man and woman. He inserted the Y into man's name, turning esh (fire) into i-Y-sh (ish, man); and H into woman's name, making i-sha-H (ishah, woman). The Chronicles of Yerahmeel (6:16) comment on this: "If they walk in My ways and observe My commandments, behold My name will abide with them and deliver them from all trouble. But if not, I will take the letters of My name from them, so that they will revert to esh and esh, fire consuming fire." Hence with God as a partner, marriage is a blessing, ish and ishah.

The whole article is about Jewish marriage and very interesting. You can read it here.
What this means is what I have been trying to say all along: every couple has a choice between living with God, or enduring the presence of their Parent. As experience tells us, when the Parent is present in the marriage, there is no place for God. The fires of the unconscious will consume the marriage and devour the initial spark of love.
So, to all the couples getting married this season: I hope that you indeed manage to leave your Parent and I wish you a happily conscious marriage.

Here are some books to get you started on the right foot:

Further Reading For Married Couples
I'm OK--You're OK– an excellent, most useful simplification of the psychology behind our everyday interactions and thoughts.
Toxic In-Laws: Loving Strategies for Protecting Your Marriage – another gem from the author of the incredibly insightful Toxic Parents: Overcoming Their Hurtful Legacy and Reclaiming Your Life
Getting the Love You Want: A Guide for Couples – The ultimate guidance book for couples who want to save their marriage from the Parent. A step-by-step indispensable self-help book for couples. Useful even before the marriage.
A previous article on God as Self, for those of you who, like Freud, confuse God with the Parent.