someone who, for religious or spiritual purposes, practices strict self-discipline and abstains from different kinds of activities.

Ascetic.

Explanation:

We have been given a statement. We are supposed to choose one word for the given statement.

Statement: Someone who, for religious or spiritual purposes, practices strict self-discipline and abstains from different kinds of activities.

We know word ascetic is derived from Greek word asketes, which means monk, or hermit.

Being ascetic means to deprives oneself from pleasures of the world by strict self-discipline. The purpose of ascetic person is to pursue spiritual goals.

Therefore, the correct word for given statement is ascetic.