Thus, by our saying, “whose consumption is prohibited,” permissible substances are excluded. Every substance whose consumption is permissible is pure.

By our saying, “not because of its harmfulness,” poison and the like are excluded. They are prohibited because of their harmfulness, but they are not impure.

By our saying, “nor because people find it repulsive,” mucus and the like are excluded. They are not impure, because they are prohibited on account of their repulsiveness.

By our saying, “nor because of its inviolability,” game hunted while one is in the state of consecration, and game within the Sacred Precinct, are excluded, for they are prohibited due to their inviolability.

Thus, the phrase, “the disappearance of physical impurity,” is broader than “the removal of physical impurity,” because physical impurity may disappear of its own accord. For example, if we assume that some ground has become impure through urine, then rain comes and purifies it, it becomes pure without any removal on our part. Likewise, if we have water rendered impure by a change in its odor, and then the odor disappears on its own, it becomes pure. And if we have wine which turns into vinegar of its own accord, it becomes pure—although the correct view is that wine is not impure, even while it remains wine, as will come, Allah willing, in the chapter on “Removing Impurity.”

The author began with purification for two reasons:

First, purification is the removal of harm.

Second, purification is the key to prayer. Prayer is the most emphatic of Islam’s pillars after the two testimonies of faith. For this reason, the jurists, may Allah have mercy on them, begin with the Book of Purification.

Purification requires something by which one purifies oneself, through which impurity is removed and ritual impurity is lifted: namely, water. This is why the author began with it.