The derivative meaning of the word diksha is –
diyate paramam gyanam kshiyate papa karmani -
which bestows the supreme knowledge & frees oneself from all sins.
Diksha can be of two types :
1. Namajapa Diksha – this can be received by anyone easily as the Guru ( not necessarily be a Sadguru) initiates a person with Mantra as a starting point in the spiritual path.
2. Asadharan Diksha or Yoga Diksha or Kriya Yoga Diksha – this can only be obtained from a Sadguru who initiates his disciples so that they can also perceive the Supreme, guiding them from unfathomable darkness to the enlightened world. A Sadguru does not aspire after narrow material gains as He has crossed such limits. This relationship between the Sadguru & disciple is an everlasting one. The numbers of such Sadguru as well as number of followers are very very small.