Accepting a Teacher...
As devotees of Lord Krishna, we believe that both the acceptance of a spiritual teacher and living by the instruction of our sacred scriptures are essential in our development towards our spiritual goal.
God is the most powerful and great, but because of our limited ability in our materially conditioned state, we cannot approach him directly. We need the help of a spiritual teacher and the Vedic scriptures.
No matter how hard we may try, we will not be able to realize spiritual subject matter by academic study nor speculation alone. Just like when learning chemistry, law, mathematics, or art, it is so much more effective to study under a recognized expert. The same holds true for the spiritual science of self-realization.
A genuine spiritual master teaches how to raise one's consciousness beyond material bodily designations, attain real peace of mind, obtain true knowledge of the self, achieve liberation from karma and reincarnation, and how to develop love of God through the process of devotional service. And for all this a guru is not merely a help, but a necessity.
Therefore we see the spiritual teacher as a representative of God, but not because of his ability to speculate, or give opinions or interpretations on the scriptures. The Guru is respected and honored because he has perfectly heard, assimilated and realized the words of his spiritual master, who in turn heard from his spiritual master and so on. In this way, back through the chain of disciplic succession, until we come to Srila Vyasadeva (an incarnation of God) who compiled the Vedic scriptures 5,000 years ago.
In other words it is just like a postman who does not write anything personally, but rather delivers what has been written. Similarly, the spiritual teacher delivers the message without adding or subtracting any of its contents. For this reason we can accept his word as being the word of God, or knowledge that has descended from above.