Purification here means physical purification (by doing physical exercise) and inner purification (by doing forgiveness and various other techniques). Thorough cleansing of chakras and the aura. Purification increases the capacity of the physical body to handle greater amount of subtle energies. It enables the brain and nervous system to attain higher consciousness and experiences. It helps to develop inner calmness and stillness. It develop sensitivity and prolonged awareness which is needed in order to physically experience expansion of consciousness and intuitive intelligence. It helps disintegrates and normalizes the chakras and corresponding organs. Nothing is the same if we have done thorough physical and inner purification.
Like when the window of mind is not clean than it becomes difficult to find inner stillness. Purification also help in increasing the ability of your body to get heal rapidly.Proper diet and your etheric hygiene is also part of purification.
You can also learn these purification techniques and experience by yourself how it can bring change in your life.