In our previous lives, while under the influence of deluded minds, we accumulated a lot of negative karma, and we also transgressed our vows and commitments and incurred root and secondary downfalls. As a result, we now experience difficulties in developing faith and conviction in Dharma, and in making progress on the stages of the path to enlightenment. Moreover, if we do not purify all this negativity while we have the chance, we will have to experience great suffering in the future.
Any living being, even a worm or an insect, can commit negative actions; but only humans have the fortune to be able to purify them. We have been accumulating non-virtuous actions and experiencing their suffering results since beginningless time; but now we have an opportunity to purify them completely. We should make use of this precious opportunity to purify our negative karma, not to create more! Since purification is the root of future happiness and spiritual realizations, we should strive to cleanse our mind of delusions and negative karma by practising the meditation and recitation of Vajrasattva. This is a very powerful method of purification.
Geshe Kelsang Gyatso 1990