In "On My First Son" by Ben Jonson, what is the theme?

In this moving poem, Ben Jonson writes about his son,
Benjamin, who died on his seventh birthday of the plague. Thus the poem begins as you
might expect with the farewell to a dead son. The speaker regrets having forgotten that
the child was merely lent to him by God. He consoles himself with the thought that his
son is now free of the pains of living and of growing old. In the last lines, the
speaker offers an epitaph for his son, calling him "his best piece of
poetry":

Rest
in soft peace, and asked, say, "Here doth lie

Ben Jonson
his best piece of poetry;

For whose sake henceforth all his
vows be such

As what he loves may never like too
much."

He concludes with a
vow never again to "like too much" what he
loves.

Interestingly, the central ideas of death that are
presented in this poem are quite depressing. Jonson concludes that since all are to be
taken from him, he must hold himself back from loving "too much" so that when the
inevitable happens and death claims them, he is not so sad and grief-stricken as he was
with his son. Yet at the same time his comparison of his son with a poem suggests that
non of his work could ever be as wonderful as his son was to him, and indicates perhaps
a new perspective on life, showing Jonson that family is more important than his work.
Thus one of the central themes of this memorable poem to my mind is how we cope with
death and how it changes us. Jonson seems to recommend not loving "too much" in the
poem, yet at the same time his epigram suggests an emphasis on the family that clearly
indicates enjoying and loving them greatly, in spite of the fear of
death.