There are two kinds of love: the intrinsic, calm love that we feel for people to whom we're related by birth; and the more intimate, fiery love that exists in marriage. This is why the husband-wife relationship is very different from the parent-child relationship.

The love within a family, between relatives who are born of the same flesh, is innate. The love between a mother and child, a brother and sister, two brothers, two sisters, comes easily. Since they're related by nature, they feel comfortable with each other. There's an innate closeness between them, so their love is strong, solid, steady, predictable, and calm There's no distance that has to be bridged; no difference that has to be overcome.

The love between a husband and wife isn't like that. Their love wasn't always there; they didn't always know each other; they weren't always related. No matter how well they get to know one another, they aren't alike. They are different from each other physically, emotionally, and mentally. They love each other in spite of the differences and because of them, but there isn't enough of a commonality between them to create a casual, calm love. The differences remain even after they are married, and the love between them will have to overcome these differences.

After all, husband and wife were once strangers. Male is different from female, so in essence they must remain strangers. Because of this the love between them can never be casual, consistent, or calm.

This acquired love is naturally more intense than the love between a brother and sister. When love ahs to overcome a difference, a distance, an obstacle, it needs energy to leap across and bridge the gap. This is the energy of fiery love.

Because the gap between husband and wife will never really close, their love for one another will continually have to reach across it. There will be distance, separation, then a bridging of distance, and a coming back together, again and again. This sense of distance intensifies the desire to merge.

To come together, man and woman have to overcome certain resistances. A man has to overcome his resistance to commitment, and a woman has to overcome her resistance to invasion. So, in coming together, husband and wife are reaching across great emotional distances, which intensifies their love. The absence of innate love actually makes the heart grow fonder.

If a brother and sister were to have a fiery love, their relationship would suffer. It's not the appropriate emotion for a brother and sister to have. Their love thrives when it's unbroken, unchallenged, constant, and calm. Not that they can't have disagreements, but those disagreements disrupt their love.

On the other hand, if a husband and wife develop a calm love for each other, their relationship will not thrive. If they are too familiar with each other, too comfortable with each other, like brother and sister, their love will not flourish. True intimacy in marriage – fiery love – is created by constant withdrawal and reunion.

If a husband and wife are never separate, their love begins to sour, because they are not creating an environment appropriate to that love. The environment of constant togetherness is not conducive to man-woman love; it's the environment for brother-sister love or parent-child love.

That's why the ideal blessing for a married couple is, "Your honeymoon should never end." A honeymoon – when two people who were once separate come together for the first time – should never end, because that's what a marriage thrives on.

The love between a man and a woman thrives on withdrawal and reunion, separation and coming together. The only way to have an environment conducive to that kind of relationship is to provide a separation.

There are many kinds of separations. A couple can live in different places, have differences of opinion, or get into arguments and be angry at each other. Often the arguing isn't for the sake of arguing, but for the sake of creating a distance so that husband and wife can feel like they're coming together.

That's not a very happy solution. Making up after an argument may be good for a marriage on occasion, but not on a regular basis. It isn't a good idea to go looking for arguments, especially since separations can take a more positive form.

The physical separation given to us by G-d for that purpose is a much happier solution. That separation is created by observing a collection of laws described in Leviticus as "the laws of family purity," but more frequently referred to as the "laws of mikvah" (Lev. 15:19-33). The mikvah refers to the ritual bath in which traditional Jewish women, since the days of the Bible, have immersed themselves following their monthly period and before renewing sexual relations with their husbands.

According to these laws of mikvah, during the time that a Jewish woman is menstruating, and for one week afterward, she is physically off-limits to her husband. For those days, the physical separation is total: no touching, no sitting on a swing together, and even sleeping in separate beds.

Through the ages, all sorts of explanations have been given for the laws described in Leviticus, but all of them have one thing in common: Separation protects and nurtures the intimate aspect of marriage, which thrives on withdrawal and reunion.

This understanding is not unique to Jews. In most cultures throughout the world, the ancients practiced varying degrees of separation between husband and wife during the woman's menstrual period. Some, such as certain tribes of American Indians, actually had separate living quarters, menstruant tents, where a woman would stay during her period Later these customs deteriorated into myths, taboos, fears, superstition, hygienic arguments and other rationalizations, in an attempt to make sense of a delicate and sensitive subject.

But separation was such a universal practice that I wonder if human beings know instinctively that male-female love thrives on withdrawal and reunion, on coming together following a separation. The body is actually reflecting an emotional state. Just as the love between man and woman cannot be maintained at full intensity all the time, but needs a certain tension without which it will not flourish, the body has a similar need.

As far as Jews are concerned, we know these cyclical changes were created for that very purpose. This is much more than a coincidence: It is how the body reflects the soul, how the body is created in the image of the soul.

Like everything else that exists in our lives, the cycle of withdrawal and reunion that exist in marriage is meant to be a reflection of our relationship with G-d. The two kinds of love, calm love and fiery love, exist not only among human beings, but between ourselves and G-d.

When we refer to G-d as our father, it's an innate and intrinsic relationship. We don't have to work for it; it's just there. It's a steady, constant love, an indestructible love, a love compared to water – calm love.

But we also talk about how G-d is infinite and we are finite; G-d is true and we are not; G-d is everything and we are barely something. Because of these differences, we feel a great distance from G-d, and the need to create a relationship with Him. Establishing a relationship in spite of the differences, in spite of the distance, is more like a marriage. That's a stormy relationship – fiery love.

More precisely, our soul loves G-d like a child loves a parent, because our soul is of G-d. That love is innate and calm. When G-d tells this soul to go down into a body, that's a separation. Then our soul loves G-d with a fiery love, which like the love between a husband and wife, does not come automatically. Acquired love is by nature intense and fiery.

Eventually, the soul will be reunited with G-d more intimately than before, just as the intimacy between a husband and wife is deeper when they come together following a separation. Therefore, when G-d says that a husband and wife have to be modest with one another, that they may be together and then separate, come together and separate again, according to a monthly cycle, it's not an artificial imposition. It may produce discipline, which is nice. It may keep the marriage fresh, which is important. But there's more to it than that.

It is, in fact, the natural reflection of the type of love that must exist between husband and wife. In order to nurture that stormy, fiery love, our way of living has to correspond to the emotions we are trying to nurture and retain.

If there's going to be a separation – and there needs to be one – consider the following: Rather than wait for a separation to develop, where a husband and wife get into a fight or lose interest in each other, let's take the cue from the body and create a physical, rather than emotional, separation.

Everyone is saying, "I need my space." It's true. Keeping the laws of mikvah, when they apply, is one way of creating that space; other laws of modesty might be beneficial as well. For example, husband and wife need not touch each other casually or in public; they should avoid casual nudity; and vulgarities, which are inappropriate in mixed company, should also be inappropriate for the home.

In giving us these laws, G-d tells us: "The marriage love, unlike the family love, unlike the born love, thrives when you separate and come back together. But rather than create an internal, emotional separation, create and external separation by keeping the laws of modesty. Don't separate emotionally; separate physically, and come back together emotionally."

Since the love between husband and wife is one of reaching across distances, of the constant bridging of a gulf, and only that kind of intimate, fiery love is appropriate for husband and wife, our physical behavior has to reflect and support that emotional state. We do that by being modest.

Doesn't Anyone Blush Anymore: Reclaiming Intimacy, Modesty and Sexuality, HarperCollins Publishers