Does the impurity of war describe only a halachic state, or also a psychological and spiritual wound?
To your question, I should clarify that I am not an actual rabbi and have no authority to answer questions of halacha. So I am not ruling here on the laws of purity and impurity, but offering a reflective reading of the parashah.
In the plain sense of the verses, impurity is first of all an objective halachic and ritual state that results from contact with the dead. The Torah says:
“And you shall camp outside the camp for seven days; whoever has killed a person and whoever has touched a slain body shall purify yourselves on the third day and on the seventh day, you and your captives.” (Numbers 31:19)
The verse does not say that the warriors sinned by the very act of taking part in the war, nor does it explicitly describe emotional trauma. So it would be inaccurate to claim that corpse impurity is simply a biblical name for a psychological wound.
But here the reflective reading begins.
The parashah does not allow the warrior to pass directly from the battle into the camp. Even after victory, and even when the war was waged by command, there is a pause. There is distance. There is time. There is purification. Only afterward does one return to ordinary life.
From here one may offer a derashah: the Torah does not treat contact with death as if nothing happened. The warrior does not return at once to routine like a person who has been through nothing unsettling. Even an act performed as a duty may leave a deep impression, and so an orderly passage is required, from death back to the camp, the family, and life.
The astonishing point is that impurity is not necessarily blame.
The warrior may be right, loyal, and a messenger of the public, and still be impure. In other words: one can do the required thing and still need purification.
This is a great insight about the human soul. Not every wound testifies that you did something wrong. Sometimes it testifies that you met a reality too harsh to pass through unharmed.
There is also meaning in the fact that not only the people undergo a process, but even the garments and the vessels. On the halachic level these are the laws of purity. On the homiletic level one can see here a statement that war touches everything a person carries: their body, their belongings, their memories, and their surroundings.
So the precise answer is:
In the plain sense, this is a halachic state of purity and impurity. But as a spiritual reading, one can also see in the process a recognition that contact with death leaves a mark, and that returning from war demands time, a boundary, and a process of coming back to life.
This is an interpretive idea, not an explicit reading of the verses.
More questions and answers on Parashat Matot:
What does the fact that only a thousand warriors from each tribe were sent to war teach us?