When you preserve something, you maintain its condition, like trying to preserve your good health by exercising regularly and eating right.
The verb preserve describes keeping something as it is now, without a decline in quality. It can also refer to keeping something safe from harm, as in “The group worked hard to preserve the regional ecosystem.” When you preserve food, such as fruit, you keep it from rotting. Jellies and jams are preserves, the noun form. A preserve can also be lands set aside, or preserved, as animal habitats.