In this week's parsha, Matos, we read about the victory over Median. Then we are taught the laws of how to purge vessels (kashering), which is to purge them of any non kosher foods that have been cooked or baked in them, and the law of submerging vessels (toiveling), which is to submerse them in a mikvah or into a body of water suitable for submersion. This was relevant to the war against Median, because in the booty from the war, there were many vessels, and if they wanted to use them for food, the vessels would need purging and submersion.
The Ramban asks, why weren't the laws of purging vessels taught earlier, after the wars against Sichon and Og, mentioned in parshas Chukas? There were definitely vessels in the booty captured in those wars.
The Ramban answers, that because the lands of Sichon and Og is part of the land given by Hashem to the Jewish people, all of the booty was permissible to them, even things that are normally forbidden... And our sages say, "dry meat from pigs were permitted to them," but Median was not theirs, they didn't take their land... Therefore their vessels were considered forbidden.
That is why these laws were taught here, because now they became relevant.
There is a question on this Ramban. Why does he only ask about purging vessels? The same question could be asked about submerging vessels. How come it wasn't taught earlier by the wars against Sichon and Og?
Purging is to remove the physical forbidden flavor that was absorbed into the walls of the vessel. Submersion is for removing spiritual impurities from the vessel. In the wars against Sichon and Og things that were usually forbidden were permitted. But when it comes to submersion, any vessel used for food, that transfers from a gentile's possession to a jew's, needs submersion before he can use it, even if it is brand new. It would make sense to say, that the vessels from the wars against Sichon and Og, needed submersion. So why wasn't the law of submerging vessels taught by Sichon and Og?
To understand this, we need to understand why a vessel we get from a gentile needs submersion, even if it is brand new.
Rashi explains about submerging vessels, that the simple explanation is, that submersion is to remove spiritual impurities. And he continues to explain that Elazar told the Jewish people, that vessels need purging to remove the forbidden flavor that was absorbed into them and submersion to remove the spiritual impurities. Then he says, "Our Rabbis learned from here, that even to make them ready for use, from being impermissible (issur), they need submersion." The sages use the term issur, which doesn't refer to impurity, but rather to something that is not kosher. But isn't that what purging is for? How does submersion help take the vessel from a state of not kosher to kosher?
When a vessel is in a gentile's possession, even if it is brand new, it has the possibility to be used for issur, not kosher. Even if he doesn't use it, it is considered in a state of issur, because it has the possibility to be used for not kosher. When a Jewish person takes possession of the vessel, it doesn't have the possibility to be used for issur any more. To take it out of its previous state of issur, it needs submersion.
Now we can understand why the Ramban doesn't ask, Why weren't the laws of purging vessels taught earlier, after the wars against Sichon and Og? Because the answer is the same. Being that the concept of issur was suspended in those wars, that even "dry meat from pigs were permitted to them," nothing was in a state of issur, therefore nothing had to be submersed.
This will also clarify some other ideas.
When we sell our chametz before Pesach, it is sold to a gentile. If a vessel is among the items being sold, then after Pesach, when the chametz is bought back from the gentile, the vessel doesn't need submersion. Why not? Doesn't his purchase put the vessel in a state of issur?
The answer is, that it does not. Being that the sale is done with the intention to buy it back after Pesach, it doesn't enter a state of issur. Even though he can potentially come and take it, the reality is that he doesn't. It is therefore extremely unlikely, if not impossible that he will come to use it. Also, according to many, the sale is a kind of trick, nevertheless, it works for not having chametz on Pesach. So it doesn't need submersion.
On Shavuoth we have a custom to eat dishes made with dairy products, milk, cheese, butter, etc. One of the reasons for this tradition, is because on Shavuoth we received the Torah and became obligated to keep the laws of ritual slaughter (shechita), and only one who is obligated to keep these laws can do them. So none of their meat was kosher to eat. They couldn't slaughter new meat because according to all opinions, it was Shabbos and on Shabbos we are not permitted to slaughter. But they didn't have these issues with dairy, so they ate dairy.
It is certain that the dishes they ate were prepared in vessels. Before the giving of the Torah, they were not obligated to separate milk and meat, so they would need to be purged. And even if they had vessels that are normally used only for dairy, it would seem that they would need submersion before they could use them, because they had the possibility to be used for issur. If so, how were they able to use their vessels?
When the Jewish people left Egypt, they knew that the purpose was to receive the Torah. Therefore they already started to keep some of the laws. One of the laws they kept, was separating milk and meat. Being that this was the case, their vessels were not in a possible state of issur before the giving of the Torah. Therefore they didn't need submersion.
So it seems that there are two reasons for submerging vessels, to purify them from spiritual impurities, and to change their status from forbidden to permissible.
Every mitzvah we do is precious to Hashem. Some may seem more important than others. For example, we can easily understand purging vessels, it makes sense, it is even scientific, but it is harder to wrap our heads around the mitzvah of submerging vessels, which is more spiritual in nature and we don't see the change in the vessel. Perhaps when Moshiach comes, and our spiritual awareness is heightened, we will see and understand the spiritual.
For now we do them just because it is what Hashem wants, and that to Him, is most precious of all.
May the merit of the mitzvahs we do tip the scale and usher in the coming of Moshiach. May he come soon.