Rambam - 1 Chapter a Day

As stated in Hilchot Sha’ar Avot HaTum’ah Chapter 7, Halachah 1.

A se’ah is 8.3 liter in modern measure according to Shiurei Torah and 16.2 liter according to Chazon Ish. When calculating the 40 se’ah that comprise a kosher mikveh, it is customary to follow a more stringent view.
The Rambam mentions less than 40 se’ah of water, because if the pit contains 40 se’ah of water, it is considered as an acceptable mikveh and does not contract impurity, nor, needless to say, impart impurity.
The Mishnah (Mikvaot 1:1) considers such bodies of water as the lowest of six categories to which the laws of ritual purity apply.

I.e., a greater measure of leniency applies.

Water that was drawn using a container and then used by humans to fill a pool. Such water is unacceptable for use in a kosher mikveh. Nevertheless, even though it was once in a container, in this context, it is given advantages over water that is presently in a container.

Even though the impure person intended to enter the water, since he did not desire to get wet, it is considered that he came in contact with the water against his will. See Chapter 13, Halachah 5. This rationale resolves the question raised by the Ra’avad.

For these are all willful actions.

For, as stated in Hilchot Sha’ar Avot HaTuma’ah 8:10-11, a person who drinks impure liquids contracts impurity.

Our translation follows the version in the authoritative manuscripts and early printings of the Mishneh Torah. A slight printing error appears to have crept into the standard published text.

The Ra’avad questions the Rambam’s statements, maintaining that since the water was uprooted from its original place, it does not matter whether it was uprooted willfully or not. As stated in Chapter 12, Halachah 3, the Rambam does not follow that understanding and maintains that unless liquids were uprooted from their original place willfully, they do not make food susceptible to impurity.

For the original water is considered as batel, negligible, in comparison to the new water that collected.

We assume that a majority of the water there at this time is rainwater. Moreover, we do not suspect that the rainwater itself contracted impurity, for during the rainy season, it is not likely that passersby will drink from water collected on the ground.

Since these bodies of water contain less than 40 se’ah, they are susceptible to impurity and become impure because of contact with an impure person or implement.

Because until the roads dry out, it was unlikely that people would undertake longer journeys. However, from the time the roads dry out until the next rainy season, these collections of water are impure.

For we assume that people would choose more accessible sources of water.

E. g., a horse or a donkey on which a person could have ridden (Kessef Mishneh).

For that would indicate that a person did in fact descend to the pit.

A goat or a lamb.

Without being led there or accompanied by a human.

Because the majority of the water is likely to be rain water.

Which is assumed to be impure (Chapter 2, Halachah 26).

I.e., even during the rainy season, it is possible that the majority of the water in the marketplace comes from human use.

As mentioned in the following halachah, the laws applying to other liquids are more stringent than those applying to water. Hence it is important to determine whether the mixture is categorized as water or not.

In contrast to water that contracts and imparts impurity only through willfull actions.

When the oil congeals, one might think that it is a distinct entity in its own right, separate from the water.

They can contract impurity and then impart that impurity to the water.

I.e., whether they are collected on the earth or in containers, the laws stated in Halachah 1 with regard to water in a container apply to them.

For these reasons, Mikveot 1:6 places them in a second category, distinct from the collected water mentioned previously. See Hilchot Mikveot 9:2 for more details regarding the laws that apply to them.

I.e., his hands alone are impure, as stated in Hilchot She’ar Avot HaTum’ah 8:8. Were the person himself to be impure, he would be forbidden to partake of the terumah.

It is forbidden to impart impurity to terumah. Nevertheless, since the figs after being harvested had not come in contact with liquids, they did not yet become susceptible to impurity.

A pebble became mixed with the figs he was eating and he accidentally inserted it into his mouth.

This addition is made on the basis of the Rambam’s Commentary to the Mishnah (Keilim 8:10).

For saliva is a derivative of water and equivalent to it.

By turning over his finger, he will have moved the saliva and thus uprooted it from its place. The saliva would then impart impurity to the fig because, as stated in Chapter 6, Halachah 5, when a food comes in contact with impure liquids, it makes the food susceptible to impurity and imparts impurity at the same time.

For like the water, this saliva is in its natural place.

Halachah 1 above.

And not to move the saliva. Hence, even though he did move it, it is not considered as if he did so willfully.

A Roman copper coin used in the Talmudic era, of relatively low value, worth one sixth of a dinar (Hilchot Arachin 4:3).

As the Rambam explains in his Commentary to the Mishnah (Keilim 8:10), putting the coin in his mouth will cause the person to salivate and thus quench his thirst somewhat.

As a result of an intentional act.

According to the Rambam’s understanding, this law applies even if the woman is ritually pure. The Ra’avad has a different understanding of Keilim 8:11, the Rambam’s source.

In truth, this law would apply to ordinary food as well. The Rambam mentions terumah only because of the parallel to the previous halachah.

I.e., an oven that was impure because of contact with a human corpse.

This is speaking about an instance where she held her finger inside the oven after it began to bleed or after she sucked it. The blood on her finger and her hand itself contracted impurity from being inside the oven's inner space and then imparted that impurity to the saliva and the food in her mouth [in a way parallel to that explained in the previous halachah; see the Rambam's Commentary to the Mishnah (loc. cit.:11)]. The person himself does not become impure, because earthenware containers and impure liquids do not impart impurity to humans.