Chivers: Why should I mourn?

Thomas Holley Chivers led a difficult life. Born to a wealthy family in Georgia,  he earned a medical degree but did not practice medicine and felt compelled to be a poet. His first wife left him (with his first child) and the four children he had with his second wife all died young. He also had difficulty dealing with the death of his mother and his favorite sister. As such, his poetry is riddled with melancholy and reflections on death. He frequently used the name "Isa" as a reference to a beloved daughter. His "Song to Isa" (one of a couple with that title) is dated December 4, 1841:

Why should I mourn, or weep, or sigh,
    For that Bright World to be,
Where all my tears shall be wiped dry—
When here on earth, before I die,
    I see that Heaven in thee?

If Heaven be here on earth with me,
    Then I can never die;
Or, having died, as it may be,
I am to dwell, henceforth, with thee
    In immortality.

Then let thy pensive head recline
    Upon this peaceful breast;
For, being absorbed in thine,
My soul now seems in Heaven to shine
    A saint among the blest.

The poem was printed in 1845 in Chivers's self-published book The Lost Pleiad. It is one of seven poems in the 33-page collection with "Isa" in the title.