Joseph Campbell's observations about the "Hero's Adventure" and "Spiritual Marriage" on the Power of Myth PBS series have been compelling. Here are his comments about the latter. Added emphasis appears in red, and my reactions are enclosed in a box: (Note 105)

Campbell Myth helps you to put your mind in touch with this experience of being alive. It tells you what the experience is. Marriage, for example. What is marriage? The myth tells you what it is. It's the reunion of the separated duad. Originally you were one. You are now two in the world, but the recognition of the spiritual identity is what marriage is. . . .
  When people get married because they think it's a long-time love affair, they'll be divorced very soon, because all love affairs end in disappointment. But marriage is recognition of a spiritual identity. . . . By marrying the right person, we reconstruct the image of the incarnate God, and that's what marriage is.
The internal union of hieros gamos helps ensure the external reunion in a primary relationship. By discovering splits within myself and healing them, I prepare for a spiritual identity. Otherwise my partner ends up carrying the burden of Eve, Helena, Mary or Sophia to compensate for my unresolved anima issues.
Moyers The right person? How does one choose the right person?
Campbell Your heart tells you. It ought to.
Moyers Your inner being.
Campbell That's the mystery.
Moyers You recognize your other self?
Campbell Well, I don't know, but there's a flash that comes, and something in you knows that this is the one.
The Intuitive Self knows when the spiritual partner arrives. By attending to the moment, I will have the perceptiveness to recognize the flash when it comes. If I am not listening, the flash will come and go without my noticing it.
Moyers If marriage is this reunion of the self with the self, with the male or female grounding of ourselves, why is it that marriage is so precarious in our modern society?
Campbell Because it's not regarded as a marriage. I would say that if the marriage isn't a first priority in your life, you're not married. The marriage means the two that are one, the two become one flesh. If the marriage lasts long enough, and if you are acquiescing constantly to it instead of to individual personal whim, you come to realize that that is true - the two really are one.
Moyers One not only biologically but spiritually.
Campbell Primarily spiritually. The biological is the distraction which may lead you to the wrong identification.
I have batted zero relying on biology, largely unconsciously, as the initial basis for a long term primary relationship. However inner work in search of The Intuitive Self prepared me for a metaphorical encounter with a marriage partner. My inner knowing has the answer if I am prepared to listen to and heed the message.
Moyers Then the necessary function of marriage, perpetuating ourselves in children, is not the primary one.
Campbell No, that's really just the elementary aspect of marriage. There are two completely different stages of marriage. First is the youthful marriage following the wonderful impulse that nature has given us in the interplay of the sexes biologically in order to produce children. But there comes a time when the child graduates from the family and the couple is left. I've been amazed at the number of my friends who in their forties or fifties go apart. . . .
  Marriage is a relationship. When you make the sacrifice in marriage, you're sacrificing not to each other but to unity in a relationship. The Chinese image of the Tao, with the dark and light interacting - that's the relationship of yang and yin, male and female, which is what a marriage is. And that's what you have become when you have married. You're no longer this one alone; your identity is in a relationship. Marriage is not a simple love affair, it's an ordeal. and the ordeal is the sacrifice of ego to a relationship in which two have become one.
My "youthful" partnerships were traditionally successful. But marriage in Campbell's sense did not come my way. Although I flirted with the spiritual marriage fringe through Tantra yoga, that was not accepted by my partners. Personal spiritual integration proceeded apace, but external spiritual partnering passed me by.
Moyers So marriage is utterly incompatible with the idea of doing one's own thing.
Campbell It's not simply one's own thing, you see. It is, in a sense, doing one's own thing, but the one isn't just you, it's the two together as one. And that's a purely mythological image signifying the sacrifice of the visible entity for a transcendent good. This is something that becomes beautifully realized in the second stage of marriage, what I call the alchemical stage, of the two experiencing that they are one. . . .
I fantasized about this level of maturity in primary relationship, but did not experience it. The relationship chalk drawing comes as close as I have been able to capturing the spirit of Campbell's ideas.
Moyers That's because we don't understand the two levels of marriage.
Campbell You don't make a commitment.
Moyers We presume to - we make a commitment for better or for worse.
Campbell That's the remnant of a ritual.
Moyers And the ritual has lost its force. The ritual that once conveyed an inner reality is now merely form. And that's true in the rituals of society and in the personal rituals of marriage and religion.
Commitment has always been near the top of my list: the second quality of a rewarding relationship immediately following spirituality. The images in the chalk drawing can be seen as partners standing side by side, shoulder to shoulder, with joined hands held high in mutual affirmation of their individuality and universality.
Campbell How many people before marriage receive spiritual instruction as to what the marriage means? You can stand up in front of a judge and in ten minutes get married. The marriage ceremony in India lasts three days. That couple is glued.
Moyers You're saying that marriage is not just a social arrangement, it's a spiritual exercise.
Campbell It's primarily a spiritual exercise, and the society is supposed to help us have the realization. Man should not be in the service of society, society should be in the service of man.
This spiritual exercise may or may not be a part of my lifetime. So far a level two marriage has eluded me, although I have dreamed about it. Whatever comes of that, my inner work continues. The deepening of hieros gamos proceeds with or without a partner.