Spenser's "One Day I Wrote Her Name" is one of my favorites:
ONE day I wrote her name upon the strand, / But came the waves and washèd it away: / Again I wrote it with a second hand, / But came the tide and made my pains his prey. / Vain man (said she) that dost in vain assay / A mortal thing so to immortalise; / For I myself shall like to this decay, / And eke my name be wipèd out likewise. / Not so (quod I); let baser things devise / To die in dust, but you shall live by fame; / My verse your virtues rare shall eternise, / And in the heavens write your glorious name: / Where, when as Death shall all the world subdue, / Our love shall live, and later life renew.
Spenser is at the beach (strand) with his hard-won lady love where he idly writes her name in the sand twice. When the waves come and wash her name away the second time, she remonstrates with Spenser, philosophically saying that it is vain to try to immortalize a thing (her name and by extension, her) that is mortal (her name will die with her when she dies).
Spenser protests and states that the poetry he writes to her good name will immortalize (eternize) her. By extension of immortality, he declares that her name will be written in the heaves, alluding to the seat of immortal gods of the heavens.
Spenser concludes by asserting that when "all the world," including he and she, are dead, their love will still live on and their life together will be renewed in the heavens--the place where she lives immortalized.
The main idea is his love for this woman whom he intends to--and did--imortalize with his poetry. The literary application of the individual theme is the idea that poetry is an immortalizing art and as such is of a high and inestimable value.
Spenser's romance with this woman who originally shunned him is chronicled in his Amoretti and culminated in his Epithalamion (1595).