Selfclinging is the source of all our problems.
The obscuration of defilements covers negative emotions such as ignorance, desire, hatred, jealousy, pride, stinginess, and so on. The obscuration of knowledge means the dualistic stream of thoughts related to the three realms, such as subject and object and the thoughts themselves.
Our mind has been pure from the very beginning. His Holiness The Sakya Trizin.