Sadguru is like a Mirror
The Sadguru is not limited by virtues or sins as we generally understand it to be. He is beyond any attributes (Sattwa, Raja, Tama). Shri Gurudev is pure and is beyond dualism. He comes to the earth without any debts of past lives — like an empty container. When a devotee approaches the Guru, his (the disciple’s) image is reflected within the Guru.
Like a mirror which observes everything as a silent witness, The Sadguru is able to know about the complete life history of the devotee. He is fully aware of the past lives of any devotee who appears before Him. Also, the Sadguru’s soul reflects like a mirror. The devotee is treated by the Guru in accordance with the activities he has performed (in the past).
One should not get perturbed by the external form and mannerism of the Sadguru. Internally, the Guru is always in a state of blissfulness, even when outwardly sometimes He seems to be in rage and disturbed.
The compassionate Shri Sadguru applies various methods in order to redeem the debts of past lives and to remove the pains of the devotee. The Sadguru reacts according to the thought processes of the devotee.
Shri Guru undertakes responsibility for all the virtues and sins of His disciple. When one washes clothes in the river, initially the water of the river looks dirty. However, the river clears up gradually and finally looks clean again. Similarly, even while washing away the sins of the devotee, the Guru is always pure (sinless).
Source: Excerpts from Pages 26/28/30 of Shri Guru Bhagavat, Vol. 2 by Dr. C B Satpathy