In due course of time, a particular type of knowledge may be lost or may be covered for the time being; that is the nature of this material world. A similar statement was made by Lord Krsna in Bhagavad-gita. Sa kaleneha mahata yogo nastah: In course of time the yoga system as stated in Bhagavad-gita was lost. It was coming in parampara, in disciplic succession, but due to the passage of time it was lost. The time factor is so pressing that in the course of time everything within this material world is spoiled or lost. The yoga system of Bhagavad-gita was lost before the meeting of Krsna and Arjuna. Therefore Krsna again enunciated the same ancient yoga system to Arjuna, who could actually understand Bhagavad-gita. Similarly, Kapila also said that the system of Sankhya philosophy was not exactly being introduced by Him; it was already current, but in course of time it was mysteriously lost, and therefore He appeared to reintroduce it. That is the purpose of the incarnation of Godhead. Yada yada hi dharmasya glanir bhavati bharata [Bg. 4.7]. Dharma means the real occupation of the living entity. When there is a discrepancy in the eternal occupation of the living entity, the Lord comes and introduces the real occupation of life. Any so-called religious system that is not in the line of devotional service is called adharma-samsthapana. When people forget their eternal relationship with God and engage in something other than devotional service, their engagement is called irreligion. How one can get out of the miserable condition of material life is stated in Sankhya philosophy, and the Lord Himself is explaining this sublime system.