I often ask, who comes first - the son or the father? The answer that usually is, that the father comes first. But, in reality, if you see, it's the son first, and then the father, because the name "father" comes only when there is a son. First, he is a husband and when a son is born, thereafter he is called a father. Likewise, when the disciple is enlightened with the knowledge of Truth, thereafter is when the guide is called a Guru. Before acquiring this knowledge by the disciple, there is no Guru. That is why it is said - "Gujaarshraandhkaaro hi rukaarstej ucchyate; Agyaangraaskam brahma gurureva ne sanshayah"
(Gurugeeta) It means. "Gu" is darkness and "ru" is light, so one who removes the darkness of ignorance is called a Guru.