The scriptures talks only of three entities-God, soul and maya. There isn't any scope for fourth entity. So, who is Guru in this case? Shree Maharajji explains,"the jeevatma (soul) when attains Paramatma (God) becomes mahatma (Guru)." In sanskrit, "Gu" means "maya" and "ru" means "to dispel". Guru is one who dispels maya from soul. Only through such Guru soul attains God. Without Guru no soul can get Shree Krishna's Divine love. Even Shree Krishna is bound by His own law-without Guru, God cannot give soul His Divine vision or Love or anything else.
Shree Gaurang Mahaprabhu said:
भक्त पद धुरी, भक्त पद जल, भक्त भुक्त अवशिष्ट तीन महाबल ।
एही सेवा हेते कृष्ण प्रेमा होय ॥
Partake of the devotee's (Guru) foot dust, foot wash and remnant of his prasadam (food)-these three things possess spiritual power and with these, one (soul) gets Divine love of Shree Krishna.
Listen to the full lecture by Shree Maharajji on Guru-tattwa here: