The very purpose of rebirth is for the evolution of the soul and attainment of Moksha. The evolution is only possible through spiritual progress. Spiritual progress technically commences only when the Kundalini is awakened.
The very purpose of all spiritual paths is to awaken the Kundalini. Mostly, these methods require personal efforts. The paths are known as Raja Yoga, Hatha Yoga, Mantra Yoga (Chanting of Holy words), Laya Yoga, etc. However, in the Siddha Yoga system, the Kundalini is spontaneously awakened by the grace of the Siddha Guru by a process called Shaktipat. The Siddha Guru initiates the disciple by means of touch, word or sankalpa (intention / will). Once the disciple is initiated, the practices of Hatha Yoga and Mantra Yoga spontaneously begin due to activation of the Kundalini Shakti.
When the Shakti is ignited by the Guru, the Kundalini Shakti is ever desiring to make its upward journey to the Sahastrahara Chakra. For this, the Sadhak does not need to perform any Asanas, Pranayams, Mudras, etc. While the Shakti is rising up, the Sadhak seems to perform many kriyas, which happen automatically. These are the Asanas, Mudras, Bandhs and Pranayamas. The types of kriyas are Sadhak-specific and are dependant upon his / her sanskaras. The chitta becomes stable after these kriyas. It is observed that the Sadhaks, who have never known about all these kriyas even in their dreams, seem to perform the kriyas automatically after the Guru ignites the fire in the Sadhak by awakening the Kundalini. Shaktipat paddhati or system is a very good path for people involved in Yoga. The Shaktipat system of Yoga is very easy and does not require any special effort other than complete surrender to the Guru.
The mention about Shaktipat is sparsely given in the main Upanishads, but detailed discussion is made in the Prakirna Upanishad. It is mentioned therein that Kundalini is awakened by the eye contact with the Guru, touch or intention (will). In the Kulanarva Tantra this is called the Vedha Deeksha, Shaktipat, Siddhabhishek, etc. The Yoga Upanishad describes this path as Siddhapath and Mahayog. The manner in which a tortoise looks after its egg dug and covered in sand just by sheer will, similarly a Guru by his sheer will has the capacity to bring about activation of the Kundalini shakti in a person situated/living in any part of the world!! The only essential condition is the grace of the Guru.
If a person discards his laziness, and pursues the path of Shaktipat Yoga with dedication then he would be able to make spiritual progress and the path of Mahayog is suitable for all age groups, the young, the old, the weak and the strong. An aspirant of Shaktipat Diksha must prepare himself by practicing austerities and various disciplines in order to acquire less sense of ego and more humility and self-control. Dedication in pursuing the path and reverence towards the Guru and his grace are essential requirements for progress.