In this particular backdrop, we can understand some facts. Swaha was Daksh's daughter who fell in love with Anal who was from Agni's clan. She became pregnant and gave birth to illegitimate baby in Sarpatvan. Indra and Daksh belong to same Deva clan. Daksh ordered Matrika to kill the baby, but Kartika saved the baby. Later when Parvati saw the baby, she was amazed to see such a beautiful child with ugly Kratika. She inquired and found the fact that the baby was Swaha's son. Swaha was Sati's sister and Sati was Shiva's late wife who burnt herself in her father Daksh's court. Very nurturing and motherly Parvati, who loved Shiva very much, felt sorry for Sati's sister and adopted the baby.
Later Shiva mediated between Daksh and Agni clan, so Anal and Swaha united. Because of Kartikeya's bravery, Devas made him their leader to win Tarakasura. The war between Devas and Tarakasura was the last war between them. Losing the war Asura left for south India. That is the physical aspect of the story. When story happened that time social ethics were different, and when story was told before writing, the ethics were a changed set of values altogether. Because of audiences' curiosity Sutas gave answer according to current ethics. Since it was sage Vyas' order, Sutas were telling Puranas from generations with adding more stories to them without taking out the existing ones. Sutas were manipulating it but also preserving an ancient heritage.
On metaphysical plain Agni and Swaha's union is a play between Pran (soul or energy) and desire. Agni (fire) means energy and energy is Virat. In this play, five sensed life is borne. The five face of Kartikeya are symbol of five senses. This symbolic fact can be seen in many ways in our day-to-day life. Agni needs offerings to burn continuously. When Hindu people perform any ceremony, they offer many things to fire altar and enchant 'Swaha' for every offering.
If there are no offerings, then fire would vanish slowly. Similarly the fulfillment of desire satisfies Pran. Every desire related to five senses is different. The different forms of Swaha represent the inner quality of desire. Desires have many forms and they take many forms to fulfill inner or outer needs. Human beings do all kind of things right or wrong because of desires. With their many forms, desires challenge to Pran and try to win Pran. With their many forms desires also become reason for life.
When one desire is fulfilled, yearning for another desire arises. In human beings yearning and desires become greed, and give birth to many offences. Even if body becomes weak, desires would be young. Why desires do not end with fulfillment of desires? For the life or Pran the offering is necessary but what kind of offerings?
To understand nature of desire and greed, its compulsory to have balance in life. In life Pran is the greatest element. Self-containment can be gained only after one understands the difference between real need and greed. Any life that continuously wanders to fulfill lust cannot know real truth of Pran. In life the knowledge gained from consciousness is the sixth and most important sense that is not awaken in every one.
When human being's consciousness reached at the point, where there is no difference left between forms and formless than there is no dilemma of superficial knowledge. True awakening is when all dilemmas submerge since only then desire becomes formless, and one achieves Nirvana. Also as soon as physical body dilapidates, desires become formless. That is the metaphysics of this story!