Yo o itou kokoro wa tsuki o shitaeba ya yama no ha ni nomi omoi iruran - Senzai Wakashu(English Translation & Meaning)

世を厭ふ心は月をしたへばや
山の端にのみ思ひいるらん

Roma-ji: Yo o itou kokoro wa tsuki o shitaeba ya yama no ha ni nomi omoi iruran
English Translation: Is it that a heart
weary of the world longs
after the moon?
Only toward the mountain rim
do my thoughts go sinking in
Meaning: Is it because a heart weary of the world longs after the moon that it goes on sinking into thoughts of nothing but the mountain rim, where the moon goes down?
Commentary: Book Sixteen Miscellaneous Poems I 1007

Headnote: "Topic unknown"
Is it because a heart weary of the world longs for the moon that its thoughts sink only toward the mountain rim, he asks. As the moon sets behind the mountain rim, the heart that shuns the world thinks only of entering the mountains to live in seclusion; wondering if this is because it longs for the moon, he lays the wish for withdrawal over the moon's movement.
The author, "Hōin Jisshu," was a monk of the late Heian period who held the rank of hōin, and his biography is not known in detail.
It corresponds to "tsuki o shitaite yama ni koso ire" in 1010 of this book in singing of following the moon into the mountains. Where this poem sings of the heart that wishes to enter the mountains, 1010 sings of one who actually enters them.

First line, "yo o itou": "weary of the world," expressing the wish to withdraw from it.
Second line, "kokoro wa tsuki o": "the heart, the moon."
Third line, "shitaeba ya": "shitau" means to long for, and "ba ya" adds the interrogative binding particle "ya" to "ba," "is it because it longs?" "Ya" closes with "ran" in the fifth line. It answers "tsuki o shitaite" in the fourth line of 1010 of this book.
Fourth line, "yama no ha ni nomi": "only toward the mountain rim where the moon sets."
Fifth line, "omoi iruran": "iru" is a pivot word meaning both the moon's setting behind the mountains and "omoi iru," to be deeply absorbed in thought, also suggesting entering the mountains. "Ran" conjectures a cause, "why its thoughts sink in."
Author: Jisshu
Source: Senzai Wakashu
Prev Poem: Matsu hodo wa itodo kokoro zo nagusamanu Obasuteyama no ariake no tsuki
Next Poem: Sabishisa mo tsuki miru hodo wa nagusaminu irinan nochi o tou hito mo gana