True knowledge means understanding the distinction between matter and spirit, the temporary and eternal, the body and the soul. The Bhagavad-gita (4.34-39) teaches that one should approach a guru to understand this knowledge, and (7.2) states that knowing the Supreme is perfect knowledge. The Bhagavad-gita (13.2-3) explains the difference between the body and the soul. Material knowledge deals with temporary phenomena, while spiritual knowledge concerns eternal truth. The Science of Self-Realization (Chapter 1) elaborates that the highest knowledge is knowing the Supreme Personality.