I don't know if I agree that this is a spiritual practice because spiritual is a vague word. Having said that the formal training is like learning to make bread. Most of us start out with a recipe that we know works. Usually from someone who is an expert at making bread. After learning the recipe and becoming a expert bread maker we can make our own variations on the original recipe. But the basics are always the same. That is where formal training comes in handy. Also having a teacher keeps beginner delusions of grandeur or doubt in check.