So,in order to enter the door to God , we need the spiritual knowledge .
Spiritual knowledge is stored for us in the holy books like Vedas ,Upanishads ,Bible, Gita and Koran . When we study those holy books , we understand it according to our own IQ or our mental capacities . We twist and pervert the words on our way to extract some meaning . This way nobody can acquire the pure knowledge ,put inside it .
A teacher or a master can extract the exact meaning out of it and distribute it to us.
The important thing is to get a true master . He should be one who practices what he preaches .
One may have a teacher who teaches from books , like a first class science teacher who proves theories in a lab and his life and characters are dubious .
But the spiritual masters are different . They don't just give us spiritual rebirths . They guide us through out our lives .
The master's lab is his life . He is like Lord Krishna ,Buddha or Christ ,who know themselves completely .
They take their disciples where they go spiritually .They are the mediums which make the Unmanifest manifest.
It is the result of merits accumulated over many births to meet and get mercy of such a true master .