"And we sent thee not save as a Mercy to the worlds." (Quran 21:107)
"Sayyidna Muhammad (as) ... bequeathed to his Community a living element of his Person, and he did so by his Hand, during the two meetings at 'Aqabah; and in particular with regard to 'Ali, Abu Bakr, Salman, and Anas." (Shaykh Isa, Text 750)
Concerning the topic of initiation proper, it seems that there are three layers of interpretation that have come down to us as a superimposition upon the primitive practice of bayah as it was administered in the Darqawiyyah-Alawiyyah tradition.
As related to me by a muqaddam of the Alawiyyah-Habibiyyah order, bayah has our conventional meaning of a pact made with God in emulation of the pact made with the Prophet - may peace and blessings be upon him. The transmission of the Tariqah proper, however, coincided with the transmission of the Wird. To receive the Tariqah traditionally meant to receive the Wird. The use of the Unique Name, as they call it, historically belonged to the domain of ithn, not to that of initiation. We seem to do things a little backward by comparison, downplaying the significance of the Wird, and exalting the centrality of the Divine Name in conjunction with bayah.
I believe that this is due in large part to the three interrelated layers of interpretation arising from the evolution of ideas introduced by Guenon and successively reinterpreted by Shaykh Isa and Shaykh Hossein, perhaps also by a conscious decision made by Shaykh Isa.
From Guenon come the ideas of traditional filiation and initiatic transmission. For Guenon, traditional filiation originally meant ritual fidelity and participation in a legally chartered Masonic or quasi-Masonic lodge but the idea is also conformable to the possession of a silsilah and the preservation of the rite and formulae of the bayah. He taught that by following the prescribed rules, the ritual may serve as the vehicle of an indeterminate spiritual influence, what I interpret as essentially a magical or supernatural power or what Greg Goode calls EBT or energy-based transmission.
Shaykh Isa then developed these ideas but what was originally conceived as as a kind of supernatural power now became an equally indeterminate "special grace" that possesses a clearly defined function, to bridge the disjunction between the empirical ego and the primordial intellect.
Once again, Shaykh Hossein took up these ideas, this time applying to them a Shi'ite definition and interpretation. Under Nasr, initiatic transmission is conformable to the transmission of sanctity and authority (wilayah/walayah) throughout the lineage of the Imams.
I could be wrong, but I don't believe that the original practice of initiation into Sufism carried all of these quasi-magical and Shi'ite associations, all transmission taking place by virtue of the Wird itself which in conjunction with the bayah served as a concrete link to the silsilah, as when Shaykh Darqawi stated, "On the night of the day I met the Shaykh and took the wird from him" - each name of the silsilah like a bead upon the tasbih.
This is something that you may wish to investigate in response to those who are fixated on the idea of graces emanating from the Shaykh as a central fixture of Sufi spirituality.