What is the role of the Guru in a spiritual aspirant's life?

What is the role of the Guru in a spiritual aspirant's life?

Satchidananda Himself is the Guru. [...] when the vision of the Ishta is about to take place, the guru appears before the aspirant and says to him, 'Behold! There is your Ishta.' Saying this, the guru merges in the Ishta. He who is the guru is also the Ishta. The guru is the thread that leads to God.

Reference: The Gospel of Sri Ramakrishna (8.2 The Master's Birthday Celebration At Dakshineswar)