Analysis of An Unmarked Festival

There's a feast undated, yet
Both our true lives hold it fast,--
Even the day when we first met.
What a great day came and passed,
--Unknown then, but known at last.

And we met: You knew not me,
Mistress of your joys and fears;
Held my hand that held the key
Of the treasure of your years,
Of the fountain of your tears.

For you knew not it was I,
And I knew not it was you.
We have learnt, as days went by.
But a flower struck root and grew
Underground, and no one knew.

Day of days! Unmarked it rose,
In whose hours we were to meet;
And forgotten passed. Who knows,
Was earth cold or sunny, Sweet,
At the coming of your feet?

One mere day, we thought; the measure
Of such days the year fulfills.
Now, how dearly would we treasure
Something from its fields, its rills,
And its memorable hills.