Excerpt from the Shiva Sutras: The Supreme Awakening, by Swami Lakshmanjoo, Second awakening, verse 6.
These two powers can be attained only through the master (guru), no one else.
But who is the master?
The one who demands that his disciples donate money to him or who requires his disciples to provide service to him, all in the guise of attaining enlightenment, is not the guru.
Then who is the guru?
The guru is that person who puts before you the reality of God consciousness. It is said that the guru is the means here because only he can make you realize the fullness of these two awarenesses, mudrā and mantra.
It is declared in Mālinīvijaya tantra:
Lord Śiva tells Pārvatī, “That master who is the cause of your attaining the creative energy of Lord Śiva and who then establishes you in that state is as good as me.” (Mālinīvijaya tantra 2.10)
In other words, that master is one with Lord Śiva. In Spanda Kārikā, this point about the master is not discussed; however, in the last verse there is this reference.
I bow to that supreme and wonderful word of the master that gives rise to manifold ways of supreme thought that carry the disciple across the ocean of all doubts. (Spanda Kārikā 4.1)
Some other masters think, because of the teachings of the Mālinīvijaya tantra, that the master is not a worldly being. For them, the master is, in the real sense, the supreme energy of Lord Śiva. In this regard, it is said in Mālinīvijaya tantra:
That is the wheel of all energies and that is the mouth of the master where everything is obtained. (Mālinīvijaya tantra)
In the Triśirobhairava tantra, it is said:
The great energy of that great Lord is said to be the mouth of the master; hence, that energy, being the cause of understanding, is the means (upāya). (Triśirobhairava tantra)