In fact, that person who is not tossed about by sense experiences and always stays balanced in pain and pleasure is fit to experience immortality. 1 - The Bhagavad Gita (II:15)
The five kleshas together are like an iceberg; only a small part is visible. The tip of our klesha-iceberg is that part we can see above the surface: raga, (craving, desire) and dvesha (aversion, hatred). Lurking beneath the surface are the sneaky asmita (egoism), and abhinivesha (fear of death, clinging to life). At the core of the iceberg is avidya (ignorance, lack of spiritual wisdom).
So here I am crashing into the tip of the iceberg caught between raga and dvesha. In contrast to the opening quote from the Gita: I find myself "tossed about by sense experiences..." and I find difficulty in becoming "balanced in pain and pleasure". Maybe there's a way I can remove this iceberg from the ocean so I can see what's under the surface? Maybe I can start to melt this ginormous block of ice? This is where Kriya Yoga comes in handy.
Kriya Yoga provides the practitioner with the tools to dissolve this massive iceberg. For the purpose of study it is useful to break Kriya Yoga down into its three parts, but in practice all three parts should be integrated in order to work together. Imagine tapas as a blow torch that begins the melting process. Svadhyaya is the sword that can slice off a chunk of iceberg that we want to work on today. Put that chunk in a large cauldron and keep dicing it with the sword. Keep the blow torch going as well and soon it will be water. Then cover with a tight lid like a pressure cooker. Boil the water into steam. Then the steam can be released through that hole in the lid: isvara pranidhana. So there you have it, all three parts of Kriya Yoga working together for a common purpose: to overcome the kleshas.
1. As translated by Sri Swami Satchidanda. The Living Gita. Yogaville, 1988. (pg. 14).