Poem

Death's second self, that seals up all in rest.
In me thou see'st the glowing of such fire
That on the ashes of his youth doth lie,
As the death-bed whereon it must expire
Consum'd with that which it was nourish'd by.
This thou perceivest, which makes thy love more strong,
To love that well which thou must leave ere long.

Could you please explain this poem to me?

Thank you very much in advance.