When I first got to know about Varjayana, I was shocked by the way they respect "their" lama. They treat their Lama (Human) as a Buddha. They have their Lama picture on the throne, and we make prostration to the throne first instead of altar where Buddha is. Later when I got to know more about "their" culture, and the reason why they treat their lama as a Buddha.
One of the senior student told me that time, a Buddha statue is a representative of Buddha's enlighten body and a lot of other deep meaning, but to understand that we need an intermedium who totally understand the Buddha teaching and surpass the message to us. In this case, a qualified (by the monastery) guru will be the intermedium, who doing the same "job" which Buddha Shakhamuni have done 2500 years ago. A qualified dharma teaches must hold his vows, have a compassion mind and totally understand the inter, outer and secret meaning of Buddha teaching, since he or she have no different compare to the Buddha Shakyamuni, we should treat them just the way we treat Buddha shakyamuni.
To celebrate one lama's birthday have no different compare to celebrate Buddha's birthday. For any lama who have total control of their mind, birth and death, when they choose to be reborn in our world on certain day must be a reason. We celebrate their birthday because they have choose to come back and benefit all sentient beings again, this have no different compare that we celebrate Buddha's birthday.
It's very lucky that we are able to celebrate lama's birthday or makes any offering to them, the merit that we collected will be the same as we make any offering to Buddha. The culture that I felt weird before have become my culture now, I'm lucky to meet my guru, because he have no different compare to Buddha Shakyamuni.
This is just what I have understand so far, please share more if anyone have other understanding.