"Facing the Forests" by A. B. Yehoshua emphasizes several themes or issues in the story. What are the two main themes of the story?

The two main themes of the story are the inevitable violence that results from the limitations of speech and the corroding nature of inter-generational strife.
In the story, a lonely graduate student takes a job as a forest ranger or "fire watcher." He is tired of toiling at his academic studies; "words weary him," and he believes that a job will divert him from his increasing paranoia about life. He is hired by the head of the Afforestation Office, and after signing the necessary employment forms, finds himself engaged in awkward conversation with the manager. Soon, he is sent to work at a larger forest, but the imposing trees overwhelm his senses when he gets there. He initially feels suffocated by the claustrophobic effect of the forest but soon becomes fascinated by the tall pines.
The student's servant at the fire-watch tower is an Arab, whose tongue was cut out during one of the Arab-Israeli wars. The Arab servant represents the Palestinian "voice" of the Israeli-Palestinian conflicts. Although the text does not tell us which side cut out his tongue, the Arab's muteness symbolizes the limitations of speech in the event of a struggle for political-religious relevance. Words fail during such times, and violence becomes the only mode of communication.
In the silence of his new life, the student begins to appreciate the woodland scenery his room overlooks. He is surprised to learn that there has not been a fire in the area for several years. Eventually, he also discovers that everyone is suspicious of his Arab servant, who is suspected of stockpiling kerosene for the purposes of burning down the forest. In fact, he compares the old Arab to a "silent dagger" as he moves about in the shadows of the dark forest, poised to unleash violence on humanity.
Eventually, the Arab sets fire to the forest, rushing through "the trees like an evil spirit." The student knows that the fire was inevitable, and he does nothing to stop it. In the aftermath, the smoldering forest represents the silenced voices of generations of Israelis and Palestinians who have continued the conflict of their fathers. This inter-generational conflict has eroded trust and goodwill; there is oppressive silence instead of accord, and peace is elusive. Significantly, the books in the watchtower have been burned to ashes; there are no words to quell the anger of generations of Israelis and Palestinians. The fire is a representation of the poisonous anger that grips the entire nation. 
So, through his story, A.B. Yehoshua explores the themes of inter-generational conflict and how limitations in speech result in violence. The Israel in Yehoshua's story is bereft of its former glory, as both Israelis and Palestinians grapple with the question the story asks: "Well, what now?"
http://www.laits.utexas.edu/doherty/words2.html

https://www.encyclopedia.com/arts/encyclopedias-almanacs-transcripts-and-maps/facing-forests-mul-hayearot-b-yehoshua-1968