We are used to operate in our life from the Self, a mini me character that is operating in our head from wich we over- identify with our thoughts, feelings and the body which leads to all kind of suffering and neurosis. All spiritual practice opens us to the bigger reality of awareness, the ground of being, where the identification with the self step back and we feel a freed up and liberated way of being. Usually we quickly fall back in the old operating mode from the self, since we actually don't realize where we were and how we got to a more liberated state.
When you start with yoga, meditation or mindfulness training you will so get glimpses of awakend states, but you will very likely not be able to stabilize them, because the mind needs to be trained first and understand where he can go. Secondly most other people around us usually are not in an awakened state and therefore support us coming back into operating from the limited thinking self. Although nature is in an awakened state all the time, but we are not able to see it, because of our ego-centered conditioning in western society for centuries. Of course we are also a part of nature, but our dual view of the world separates us from natures and doesn't allow us to see the unity of all things.
To practice with a teacher is therefore the best way to remind us and helps us to access our true nature, the non-dual awakened state of awareness. He/She will give you the keys and practices to guide you on your way, according where you are.
It is said that the spiritual teacher, or the teaching finds you when you are ready. It is also said to disregard or disrespect a teacher or a teaching is one of the biggest karmic debts you may pile up: it will have you wander around in the wastelands bare of spiritual teaching for many cycles without finding a teaching again. A humble and egoless conduct is usually the best sign of a good teacher and also the best way to approach your teacher or any teaching in life.
To all the great teachers that are out there!