Vichara means you have to think. The mind is constantly thinking. It has become habitual to imagine something or other. Imaginations are called thoughts. The mind is a bundle of thoughts, in fact. So the advice is that when the Vichara has to come, let that Vichara, or thought, be a noble one, so you try to think about your Self. Just like, as a child, I used to think, "How is it that I am that Soul beyond the existence of this physical body? Am I born along with the physical body? And am I going to become extinct when the physical body dies? If at all, I am the Soul then why is it that I am not conscious of myself as that Soul? I am conscious of only the body at the moment? This is the way Vichara or inquiry should go. "Who am I?" means, how do I exist? What is my nature? These type of thoughts should keep coming and never allow these types of thoughts to die down as long as you don't get into the sadhana. After a certain stage you must get into the sadhana after this Inquiry. "Who am I?" means keep thinking within the mind, think about the Atma, think about how you exist as the Atma. Think about who you really are, are you this physical body, or are you something else? Like that you keep thinking and thinking, so ultimately you get into the sadhana.