Salt is used in the process of making soap primarily to aid in the saponification process, where fats or oils are converted into soap. When salt is added to the soap mixture, it helps to draw out excess moisture and solidify the soap, resulting in a firmer texture. This is particularly important for ensuring that the soap can hold its shape and is easier to cut into bars.

Additionally, salt can enhance the cleansing properties of soap by helping to create a more stable lather. It can also act as a natural preservative, extending the shelf life of the soap by inhibiting the growth of certain bacteria and molds.