Everyone acts under the dictation of the ego. Therefore Lord Siva is trying to purify false egotism through the mercy of the Supreme Personality of Godhead. Since Lord Siva, or Rudra, is himself the controller of egotism, he indirectly wants to be purified by the mercy of the Lord so that his real egotism can be awakened. Of course, Lord Rudra is always spiritually awake, but for our benefit he is praying in this way. For the am spirit soul. But in its actual position, the spirit soul has devotional activities to perform. Therefore Lord Siva prays to be engaged both in mind and in action in the devotional service of the Supreme Lord according to the direction of the Vedas. This is the process for purifying false egotism. Cetah means knowledge. Without perfect knowledge, one cannot act perfectly. The real source of knowledge is the vacah, or sound vibration, given by Vedic instructions. Here the word vacah, or vibration, means the Vedic vibration. The origin of creation is sound vibration, and if the sound vibration is clear and purified, perfect knowledge and perfect activities actually become manifest. This is enacted by the chanting of the maha-mantra, Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare. Thus Lord Siva is praying again and again for the purification of body, mind and activities through the purification of knowledge and action under the pure directions of the Vedas. Lord Siva prays to the Supreme Personality of Godhead so that his mind, senses and words will all turn toward devotional activities only.