Why do cats purr? What does it do energetically for the animal and perhaps for anyone or anything nearby?

This is a genetically programmed aspect of cat behavior that is part of their makeup as a created being. Like dogs, they are bringers of love. But unlike dogs, they do not have the more human-like personality and desire for frequent interaction and closeness with the humans in their environment, with a state of dependency that fosters being given attention, too can win over the person with their charms and allow them to experience loving thoughts, which is their mission after all—to bring love to the human. Cats do this in a different fashion; it is less through more complex behavioral interactions than to simply be content to be in the environment and to radiate feelings of love—both in terms of intuitive outreach as well as the behavior of purring, which creates a soothing sound and quickly is learned to be a manifestation of contentment and inner peace and happiness. This has a soothing effect on all present and that too is the purpose. It is the bestowing of love in a special, species-specific way to anyone close by. They will see the evidence of love in action—feeding the cat and causing it to vocalize its pleasure when the purring is in response to a human showing affection through holding the cat or stroking it. This indeed becomes a dance of love and a direct demonstration and payback of the pleasure being experienced. This is much like the tail wagging of the dog, which the human quickly learns to represent the emotional state of the animal and is a feedback mechanism to bring the human and animal in tune with one another. Both are signs of acceptance, both convey happy thoughts and feelings and create a mutual vibrational partnership in the moment.