Since an ordinary living being is materially contaminated, his words and intelligence are also material. Therefore he cannot ascertain the Supreme Personality of Godhead by manipulating his material senses. The conception of God derived through the material senses is inaccurate because the Supreme Lord is beyond the material senses, but when one engages his senses in devotional service, the eternal Supreme Personality of Godhead is revealed on the platform of the soul. When that Supreme Godhead becomes the aim of one's life, one is said to have attained spiritual knowledge.
The Supreme Brahman is the cause of all causes because He originally existed before the creation. He is the original cause of everything, both material and spiritual, and His existence is independent. However, the Lord has a potency called avidyā, the illusory energy, which induces the false arguer to think himself perfect and which induces the illusory energy to bewilder the conditioned soul. That Supreme Brahman, the Supersoul, is very affectionate to His devotees. To bestow mercy upon them, He discloses His form, name, attributes and qualities to be worshiped within this material world.