Generally, spiritual knowledge retires religious practice, as one's heart is purified through such practice. This has already been taught in the first six chapters of the Gita. However, the knowledge to be discussed in this chapter has been described here as religious. It is religious life in transcendence, knowledge that delivers one from material duality in the form of its eternal religious expression - devotional life. The knowledge that is pure devotion is supremely purifying.
Purification involves the clearing of karma.
Our karma exixts not only in terms of that which we are presently experiencing, it is also stored in seed in the form of desire and acquired tendencies. Whereas knowledge of the self has the power to destroy karma before it bears fruit, it cannot change one's manifest karma. Pure devotion, on the other hand, can clear even one's 'prarabdha karma', that which is already bearing fruit in this life. Krsna says that this knowledge is easily or happily preformed, as was pointed out in the previous chapter. At the same time, it is imperishable.