According to publications of Theosophy, Lord Sanat Kumara is an "Advanced Being" at the Ninth level of initiation, who is regarded as the 'Lord' or 'Regent' of Earth (The Head of The Spiritual Hierarchy for Planet Earth) and of the humanity, and is thought to dwell in Shamballah.
Scriptures, especially the Mahabharata, say that it is Sanath Kumara who comes down to help the Divine Plan of Creation, when Lord Krishna came to be. He was born to Lord Krishna as his son, and he was named Pradyumna. Sanath Kumara incarnates himself through the Divine Mother Rukmini as Pradyumna. On completion of his work, He again gets back to his original position and takes to the seat in Shambala as Sanath Kumara. Sanat Kumara is also documented as one of the four Kumaras, the first four mind-born sons of Brahma who are most famous for cursing Jaya and Vijaya.
Sanat Kumar was reborn as Lord Shiva’s son, Kartikya as part of a test that Lord Shiva had conducted. When both Mahadeva and Parvati Devi reached his hermitage, Sanat Kumara didn't notice them as he was meditating. After waiting for a long time, Mahadeva decided to test Sanat Kumara and flew into a rage. He scolded Sanat Kumara saying that his conduct did not befit him, the son of Brahma. When Sanat Kumara was addressed thus, he opened his eyes and said, "I won't be frightened by your curses, nor will I be excited by your boons. I have conquered both fear and excitement, thus you cannot make me react in any way, either ordinary or extra-ordinary." When he had replied thus, Mahadeva was pleased and asked him to seek a boon. Sanat Kumara laughed and said, "O Great Lord, Mahadeva, I cannot be agitated by illusions or illusionists, just like hurricanes cannot disturb the sky. Therefore, I seek this boon that, if you have any wish, you may seek it from me. Upon hearing this, Mahadeva said 'Om' and continued, "If you shall grant my wish, then become my son!" Sanat Kumara smiled and said, "I shall become your son”.
((Answer for Kalpana: Her question - What is summerland? ))
Many different religions have mentioned about Summerland. They all have the same concept but it will be nice to know the exact terms they use. Hence I am writing a detailed description about it. Hope it answers your question. I am putting references below so that you can read in detail about it from the books.
In Theosophy, the term "Summerland" is also called the Astral plane Heaven. It is depicted as where souls who have been good in their previous lives go between incarnations.
Theosophists believe the Summerlands are maintained by hosts of planetary angels serving Sanat Kumara, the Nordic alien from Venus who Theosophists believe is the governing deity of Earth and leader of the Spiritual Hierarchy of Earth. Sanat Kumara is believed to rule over our planet from the floating city of Shamballa, believed by Theosophists to exist on the etheric plane (a plane between the physical plane and the astral plane), about five miles (8 km) above the Gobi Desert.[1]
Theosophists also believe there is another higher level of heaven called Devachan, also called the Mental plane Heaven, which some but not all souls reach between incarnations — only those souls that are more highly developed spiritually reach this level, i.e., those souls that are at the first, second, and third levels of initiation.[1]
The final permanent eternal afterlife heaven to which Theosophists believe most people will go millions or billions of years in the future, after our cycle of reincarnations in this Round is over, is called Nirvana, and is located beyond this physical Cosmos.[1] In order to attain Nirvana, it is necessary to have attained the fourth level of initiation or higher, meaning one is an arhat and thus no longer needs to reincarnate.
Wiccans believe Summerland to be afterlife. All people, except spirits who remain behind lost and wandering, go to the Summerland, even the wicked. The Summerland will be different for everyone, their own version of Shangri-La. There, they can be reunited with their loved ones, look over those they left behind on Earth, and take time to recuperate from life. Our time in the Summerland is spent processing what we learned, recovering from the hardships, walking with the Lord and Lady and being one with them, and then planning our next life.
Most Wiccans agree that when you are ready, you are reincarnated. You may choose what form you take and even a little about your situation. You decide this based upon which lessons you wish to learn in your next life. Someone who was very selfish and arrogant may choose a life of humility to humble themselves, for example. People even choose lives of hardship in order to learn their lessons, although they don't get to plan specifically what the circumstances will be.
Wiccans do not believe in Hell or in an eternity of punishment for one life-time of sin. Some, however, do believe that you may be punished for the harm you do. Whether or not Wiccans believe in angels and demons depends upon the person. Those who do believe in such creatures each have their own opinions about them. Most practitioners it seems, believe that angels and spirit guides are simply spirits that have reached an enlightened existence after many lifetimes. They exist to guide, protect, and help humans become who they are meant to be.
Wicca is a very diverse religion. Some Wiccans believe in Reincarnation, the Summerland, or both. Specifics about these paths vary from person to person. There are different traditions of Wicca just as there are different denominations of Christianity. Many Wiccans are solitary, or prefer to practice their craft alone. All of life moves in a circle, not a straight line, like the changing of the seasons and the water cycle. It only makes sense that life itself should do the same.[2]
The essence of the Summerland is that it is a resting ground where souls can reflect on the life they led, see if they learned the lesson they had intended on learning, and then try again in due course. The Summerland is not seen as a place of judgment, but rather as a spiritual self-evaluation where a soul is able to review its life and gain an understanding of the total impact its actions had on the world. Some may believe each particular lesson (and hence, life) is chosen and planned out by the soul itself while in Summerland, whereas others may believe that lessons are planned by an external party (deities, a spirit guide, etc.).[3]
Neopaganist believe Summerland is as a place of rest for souls in between their earthly incarnations. Some believe that after one experiences life to its fullest, and has come to know and understand every aspect and emotion of physical human life (usually after many reincarnations), their deity will allow them to stay in the Summerland for an eternal afterlife, although this belief is not universal among contemporary pagans. Another common element is that the soul has little, if any, recollection of the Summerland once it arrives on the mortal plane again. The Summerland is also envisioned as a place for recollection and reunion with deceased loved ones.
As the name suggests, it is often imagined as a place of beauty and peace, where everything people hold close to their hearts is preserved in its fullest beauty for eternity. It is envisioned as containing wide (possibly eternal) fields of rolling green hills and lush grass. However, the Summerland is also viewed as the place where one goes in the afterlife in traditions of Spiritualism and Theosophy.
I think I read about it in the book ‘Laws of the Spirit World’ by Khorshed Bhavnagri. I donot remember the page number so I did not mention it here.
References:
[1]Leadbeater, C.W A Textbook of Theosophy 1912
[2][3]Rev. Daniel 'Nightwolf' Couch, MTh.