Although the poem resembles a simple folk song about thwarted love (and surely is one, the attribution to the emperor is contested), the traditional interpretation is that the poem expresses Tenji's compassion for the lot of the peasants. That is why it was considered suitable as the starting piece of the anthology. There may also have been a private reason for Teika: the surname "Fujiwara" was bestowed by Emperor Tenji on one of his ancestors, Nakatomi no Kamatari, who assisted the emperor in the overthrow of the Soga clan
in the autumn field
my makeshift hut
is only roughly thatched,
and so my sleeves
are dampened by dew
aki no ta no | kariho no iho no | toma wo arami | waga koromode wa | tsuyu ni nuretsutsu
The makeshift hut was set up in the fields where the farmers were taking in the harvest. "Kariho" is also a pun on "reaped ears." Apparently, the inhabitant of the hut expected to be joined by the one he loved, but had to spend the long night alone, his sleeves getting wet not only from the dew that falls through the gaps in the thatch, but also from his tears.
A third, but rather unconvincing reading sees this poem as an expression of mourning for Empress Saimei, the mother of Emperor Tenji, who died while leading the above mentioned military campaign in Korea.