The Chain. Willayat or the Spiritual Domain is transfered from heart-to-heart (something like transplant of a body part) rather than normal college/university styled teaching. In the Silsila, it is defined that how many times the Willayat has been transfered and from whom. To express in simple words: 'A' transfered 'B' who transfered 'C' who transfered 'D' and so on. Silsila is only active when the chain is traceable and not broken. In Silsila the Chain starts from Prophet, Peace be upon Him, then the Willayat is transfered to the Caliph Hazrat Abu Bakr, Caliph Hazrat Uthman, and Caliph Hazrat Omer. (It is noted that Khilafat is the leadership, not the Willayat. These Caliphs are leaders as well as Walis). At that time, there was no need to give is name other than Islam. The reason is following:
When the Willayat reaches Caliph Hazrat Ali, it organizes from the crude form to more organized form. This is best explained that the Prophet, Peace be upon Him, is the Sun. It is not appropriate for the Moon to shine when the Sun is above, though beyond the blue sky of the day, Moon is shining but invisible to the ground. Only when the Sun of Prophethood sets, the Moon takes over. Now the Moon rules the night. But keep it in mind that 'the Light of Moon is not its own, it is taken from the Sun which is visible to Moon but not visible to ground'. Willayat is the Moon of the night which is directly taking its light from the Soul of Prophet, peace be upon Him. There cannot be any other parable which we can provide.
Later Caliph Hazrat Ali transfered it to his special pupil(s), and so on. It reaches at Hazrat Ghaus-e-Azam who is Master of all Aulia, then it branches out. Now there are many Silsilas i.e., Qadria, Chishtia, Mulamatia, etc. Every Silsila must prove its chain linking to Hazrat Ghaus-e-Azam, otherwise it will not be considered an official Silsila, and will always lack the Treasure of Willayat, though it may be teaching good things i.e., speak truth.
It is possible to become the candidate of Friend of God through guidance from the Master. For the steady ones, there is a potential to become the Saint. The word 'Potential' is the key to understanding to whole phenomenon. All efforts and strugles only increase the 'Potential' to become Wali, but 'becoming Wali' is not guaranteed due a reason. The Willayat is first initiated and wished by Allah Himself for a person, then circimstances change for that person. That is the luck, that is a gift, which is the highest possible power after Nabuwat in the cosmos.