Q: Do you think it is possible to be both Christian and Buddhist at the same time?
A: I ... [previoiusly--see later] replied to this question indirectly when I said that belief in a Creator could be associated with the understanding of emptiness. I believe it is possible to progress along a spiritual path and reconcile Christianity with Buddhism. But once a certain degree of realization has been reached, a choice between the two paths will become necessary. I recently gave a series of teachings in the United States and one of these teachings was about patience and tolerance. At the end there was a ceremony for taking the Bodhisattva Vows. A Christian priest who was in the audience wanted to take these vows. I asked him if he had the right to, and he replied that yes, of course, he could take these vows and still remain a Christian.
I think this is a reasonable answer, especially if we understand that "a certain degree of realization" means a considerably advanced state compared to the average practitioner. To be a monk, for example, would require choosing a dominant practice, since you would be engaged in that practice all day long. However, even at that point it would still be possible, and I think beneficial, to understand how another path could lead in the same direction.
However, there is another sense in which religions should not be mixed. Traditional religions, such as Buddhism and Christianity, are associated with a lot of art, music, story, ritual, architecture, philosophy, etc. These go together and make an artistic whole that can promote strong religious experiences. In this sense, religions are like different types of food. Very few people would mix Italian and Chinese food in the same meal because it would wreak the flavours. But it is OK to go for Italian food one night and Chinese food on another night. It is also OK to favour one food over another. For example, in China, most people eat Chinese food every day, but I also noticed that a lot of people (in China) like to go for a pizza every once in a while.