A powerful, yet often misunderstood, aim of spiritual study is purity. Purity of the soul means to return to its original divine qualities. The soul has become so polluted with less than divine qualities, it can hardly enjoy being alive. Purifying the soul puts the higher self back in charge - useless and negative thoughts are removed and annoying habits finish.
A pure soul cannot be touched by sorrow; indeed the power of purity is such, it serves to remove the sorrow of the whole world. Purity restores happiness - even bliss. All you need to do, in order to re-establish your purity, is want it. But you need to want it intensely, to the exclusion of everything else.
The one thought, "I must become completely pure". sparks a fire of love between you and God. This fire melts away all the pollution, and your purity becomes such a power that it frees you from all battles for ever.