What is the purpose of the acrosome of a sperm?

Dissolve ovum shell. Dissolves outer covering of ovum (egg) after sperm comes into contact with the ovum and permits sperm to penetrate "outer shell" of the ovum. After penetration nuclei of sperm and ovum can unite before they start to divide and form an embryo.
Penetrate the egg. This allows the penetration of the head of the sperm into the female egg to consummate fertilization.