The disciple becomes like his Guru after some time by following his instructions to the very letter. If the disciple does not follow his master’s instructions and acts in a contrary manner according to his own sweet will, he is not a disciple. A real disciple is he who follows the instructions of the Guru to the very letter and spirit, who propagates the teachings of the Guru to less evolved souls in the spiritual path till the end of his life. Blessed are such aspirants.
Source: pg. 191, Sermonettes of Swami Sivananda