Pick of the Paperbacks; Final Payments, by Mary Gordon. New York: Ballantine Books. $2.75.

This is the painful, powerful, and transforming story of Isabel Moore, whose life fundamentally begins at 30, after her father succumbs to a long illness. She has spent 11 years devoting herself to his care because she sees this as simply the right and only thing to do. When this ends, she must "invent" herself anew.

The seductive safety of the predictable vs. the risk and vitality of the unplanned is one of the book's themes. Another, the central context of the novel, is religion. Isabel Moore is unashamedly and fiercely religious. The Roman Catholic Church represents to her the unattainable, the mystical, at once a source of succor and oppression. She has long ago lost her faith in ritual, but not in God. Her distorted concept of piety almost destroys her; the real thing is what ultimately saves her.