This Yoga (kriya Yoga) has as its purpose the cultivation of Cognitive Absorption (Samadhi) and the attenuating of the root causes of affliction.
An afflicted mind cannot experience Samadhi or Enstasy (Cognitive Absorption). An afflicted mind that identifies itself with the body-mind complex is by far the source of suffering.
Those root causes identification in Yoga are called the Kleshas.
In Sutra 1 of Pada 2, Kriya Yoga is described as and comprising of: Austerity (Tapas), Self-study (Svadhyaya) and Surrender to God (Ishvara Pranidhana). The practice of Kriya Yoga attenuates the Kleshas (root causes of affliction in the psyche) and also guides the Saddhak (Spiritual Practitioner) to Samadhi (Cognitive Absorption).
The more the Kleshas can be attenuated, the greater becomes the capacity of the Spiritual Aspirant to experience Samadhi. In its self, perfection in Ishvara pranidhana or Surrender to the Divine can lead automatically to Samadhi. The key is total devotion and submission to the Ideal.