Question: There are so many different schools of Buddhism, is it necessary to choose one school, or can I just accept an umbrella of them and call myself a Buddhist?
Response: If I lived in New York and had a goal of visiting San Diego, there would be many ways to accomplish my goal. I could fly, drive, ride a train, or take a bus to California. I could even walk if I wasn't in a hurry. Once I chose my means of transportation, I would then need to decide on a specific route. There are lots of options here as well.
In Buddhism, our goal is enlightenment. Our means of transportation is like a specific school. Our route is like a specific teacher.
As for my San Diego trip, if I decide to fly, book my flights in a single package through a travel service, and stick to my itinerary, I'll arrive in San Diego pretty much as planned. But if I try to combine flying, driving a car, and riding a train, and want to make all the arrangements myself, it's going to take a lot longer and be much more difficult.
It's the same in Buddhism. The Buddha taught many different ways to reach the goal. All the practice methods he taught are equally good. We just need to find the one that is most suitable for us. But if we try to take a little from here and a little from there, it will be sort of like listening to the airline ticket agent saying we need to go board the plane while the train conductor is directing us to the train. Very confusing and stressful, and who knows when we'll finally make it to San Diego. Choosing one travel package would be much easier.
In the same way, choosing one school in Buddhism makes reaching the goal much easier and will save us a lot of time.