classic waka stream

ゆくすゑの宿世を知らぬ心には
君にかぎりの身とぞいひける
Roma-ji

Yukusue no sukuse o shiranu kokoro ni wa kimi ni kagiri no mi to zo iikeru

English Translation
To a heart that does
not know what fate lies ahead
of it, the answer
is plain: you said you were theirs
and theirs alone — as I did
Meaning
To a heart that cannot know what lies ahead, the answer is plain enough: you said you were theirs and no one else's.
Commentary
62 What Did I Say to Them

A woman known as the Lady Nōsan and the priest Jōzō loved one another beyond all comparison. They had made their promises and could say everything they felt to each other, and she sent him "Omou chō kokoro wa koto ni arikeru o mukashi no hito ni nani o iikemu". The holy man Jōzō's reply was "Yukusue no sukuse o shiranu kokoro ni wa kimi ni kagiri no mi to zo iikeru". That is the whole of the section.
Jōzō was a Tendai priest, a son of Miyoshi no Kiyoyuki, known for accounts of his rites of healing. Of the Lady Nōsan the prose gives nothing beyond the name.
The setting is the same period of closeness.
What prompted the poem is hers, "Omou chō kokoro wa koto ni arikeru o mukashi no hito ni nani o iikemu", with its question about what she used to say.
This reply closes the sixty-second section. The prose passes no judgement; the section consists of the exchange alone.

What he calls the fate ahead is the working out of things not yet known; the word belongs to Buddhist teaching about bonds carried from former lives, and the priest's vocabulary shows in it.
The third line makes the general case: not knowing what is to come is simply the condition of the human heart.
The closing supplies the answer, with an emphatic particle governing its verb: you said you were theirs alone.
Where she asked what she used to say, he tells her. It is a charge that she said then exactly what she says now, and it can be read as a lover's joke in the midst of their closeness or as a priest's argument. Taking the other's question and turning it into an answer is a pattern that recurs throughout the exchanges in this book.
Source
Yamato Monogatari
Other