Exercise: Becoming the Soul
In order to purify your mind, the best thing to do is to feel every day for a few minutes during your meditation that you have no mind. Say to yourself, "I have no mind, I have no mind. What I have is the heart." Then after some time feel, "I don't have a heart. What I have is the soul." When you say, "I have the soul," at that time you will be flooded with purity. But again you have to go deeper and farther by saying not only, "I have the soul," but also "I am the soul." At that time, imagine the most beautiful child you have ever seen, and feel that your soul is infinitely more beautiful than that child.
The moment you can say and feel, "I am the soul," and meditate on this truth, your soul's infinite purity will enter into your heart. Then, from the heart, the infinite purity will enter into your mind. When you can truly feel that you are only the soul, the soul will purify your mind.