The most mysterious part of a teaching is what's known as a transmission of energy. It is a seed of spirit which the teacher plants inside the student. It can take years of regular exposure, or it can transmit in a glance. The only thing for sure is that it requires individual contact – you can't get it from a book or a video. Once planted the seed will start to grow, slowly, very slowly. Practice is simply what you do to tend and nurture and speed that growth: watering, feeding, weeding, debugging. You know you have received a transmission because it eats into every aspect of your being and your life. It cannot be escaped and only gets stronger with time. Attempts to ignore its imperatives will only produce problems later on. It has its own attendant problems of course: it becomes more and more demanding of time and energy, and there's always the risk that it will stretch your spirit to breaking point. But without a transmission there is nothing to take the place of ego, and spiritual work tends to just beat about the bush, missing the crucial point of it all, namely spirit.