Bucket of Water
From an interview with Dzongsar Khyentse Rinpoche in The Lion’s Roar:
There are many different methods for recognizing the Buddha within. Of these, the quickest and easiest is to receive the blessings of the guru. This is why guru devotion is necessary.
For example, you may be having a nightmare about monsters. But then suddenly, somebody throws a bucket of cold water over you and you wake up. The cold water doesn’t really make the monsters disappear, because there were no monsters in the first place. It was just a dream. But on the other hand, when you are having a nightmare, your sufferings are real, and the person who throws the bucket of water over you is indeed very kind and special. If you have a lot of merit you are able to meet such a person, a person who can throw the water. On the other hand, if you don’t have merit, you may never wake up from the nightmare.
The guru lineage originates with someone called Vajradhara or Samantabhadra. Our masters tell us that he is our own mind, the nature of our own mind. This means that when we trace back through the lineage, we actually end up with our own minds, the essence of ourselves. The guru is not some kind of almighty sponsor that we have to worship or obey. The most important thing to understand is that the guru is the display of our buddhanature.