It is the innate nature of the Atman. Pleasure is temporal and fleeting. Bliss is eternal and everlasting. Pleasure is mixed with pain. Bliss is unalloyed happiness.
Pleasure depends upon nerves, mind and objects.
Bliss is independent and self-existent. There is effort in attaining sensual pleasures, but there is no striving in experiencing the bliss of the Soul. The drop joins the ocean. The Jiva floats in the ocean of bliss. You will then get a proper instrument for meditation, a calm, sharp, subtle, one-pointed mind.