I don’t know in how far you are aware of what era we are in right now. Our current era is called postmodernism. One peculiar characteristic of this era is the disbelieve in any absolute truth. Rather than trusting any established religious system to provide them with something reliable and permanent to believe in, people in this era have a strong believe that everyone is supposed to come up with their own truth.
This is something very young and new. Back in the old days, telling a major religion what they are wrong about was a good opportunity to get ridiculed, outcasted or plain killed. There was a deep rooted respect for everything spiritual and people would never try to go up against religious establishment unless they are crazy or deadly committed (usually both).
These days everyone is so very confident that they understand a religion or a spiritual path well enough, that they even start calling themselves by that name within days of a celebrity announcing that he or she is spiritual now. Suddenly everyone is a Kabbalahist. The underlying reason is of course the shocking level of superficiality our society has worked itself down to. This superficiality of course is desperately needed, since otherwise our consumer culture would implode immediately.
As a result people approach spirituality these days like they approach a buffet. You can take whatever you like, as much as you like. And since fusion food is totally hip, you can very well combine sushi with cheese in a raw-vegan spring roll. And if you can do that, why stop there? Just get married as a Christian, do Yoga as a Hindu, be a Buddhist on parties and dance with your Lakota spirit at night. The confidence with which people jump spiritual trains or just make things up these days is amazing.
A friend of mine told me that once on a Sesshin, his Zen-teacher strongly admonished one of his students to stop eating like a pig at lunch. The student thereupon told his Zen-teacher that he would keep eating like he wanted and that his Zen was obviously just different from that of the teacher. Now, this answer obviously is by far the most stupid thing I have ever heard in my life, but you can see what happens to people who think they are privileged to construct there own truth.
One would think, that it is self evident why the approach of fusion spirituality is very dangerous. You are at risk to do everything without doing anything correctly.
Consider Buddhism. Buddhism comes from a very, very advanced culture. The Indian philosophies and religions we know about were a thousand years old, before the Buddha even was born. Buddhism is incredibly deep and complex. We have more then ten thousand suttas in the Pali canon alone. And Buddhism is very clear on that there is no room for personal truths. There are the teachings of the Buddha. These point to the truths. One truth. Period. No fusion necessary.
At this point you might think why is he telling me all this. Why is that relevant for me, I just want to meditate to calm my mind. Why can’t I be a Christian who also studies Buddhist meditation?
Well, yes you can. In the beginning at least. However, Buddhist meditation is pointed at enlightenment. You get there by realizing the true nature of your experiences. That everything you experience moment by moment is impermanent, unsatisfying and not self. If you don’t see that, you keep creating stuff that is artificial. Only if you let go of your clinging to artificial mental formations, you are free enough to see that the only law that governs the universe is the law of karma. This ties very closely into Buddhist cosmology and the concept of wandering from lifetime to lifetime … forever.
This is basically the >opposite< of Christianity. If you are talking to God on a regular basis, he (or she) might not be pleased with these ideas. In the eyes of God you have a permanent self that is eternal. It has to be, since you are created in his (or her) image and God is eternal be definition.
The Buddha on the other hand was >very< clear about the impermanent self. Here is how he talked to a monk who misunderstood his teachings to imply a permanent self (aka soul):
„Misguided man, have I not stated in many ways consciousness to be dependently arisen, since without a condition there is no origination of consciousness? But you, misguided man, have misrepresented us by your wrong grasp and injured yourself and stored up much demerit; for this will lead to your harm and suffering for a long time.”
[Mahātaṇhāsaṅkhayasutta / Majjhima Nikāya 38]
This, btw, is what the Buddha sounded like when he was really pissed with someone. Does that mean you cannot use Buddhist meditation as a Christian? Of course not. There is a whole MBSR-industry that was build on the foundation of selling people meditation practice without the spiritual stuff (although I cannot for the life of me figure out why anyone would want that). It just means that we should always try to be very clear and precise about who we are and what it is we are doing and why. Buddhism is all about knowing. Am I a Christian that uses Buddhist meditation, or am I a Buddhist who believes in God? The fist one is possible, the second one isn’t. The first one is not only possible, it is well established. If you have a look at the meditation practice of the Hesychasm monks, you will find there methods amazingly close to Buddhist Samatha meditation.
What exactly it is we strive for is very important, so we don’t practice something, which points in a wrong direction.