Sonnet I, the first of the "young man" or "fair youth" cycle, introduces one of Shakespeare's recurring themes:  that of the course time fading beauty and bringing eventual death.  As a solution to this dilemma, the speaker urges the "beauty" to reproduce so that "His tender heir might bear his memory" and the beauty be continued.

In the second quatrain, the speaker berates the "fair youth" for not wishing to reproduce:  "Thyself thy foe, to thy sweet self too cruel."  This charge culminates in the third quatrain as the speaker calls the youth an oxymoron: "tender churl," ["churl] is a term usually applied to ill-natured misers]who "mak'st wast in niggarding."  With contradictory images and reasoning that borders on sophistry, the speaker urges the youth to reproduce his beauty in order to preserve "his memory."  The false logic here resides in the fact that the memory cannot be the progenitor's since in death he will have no memory.  Only others can enjoy the beauty of his grown offspring.

Perhaps, then, the chastisement of the ending couple that calls the youth a "glutton" for not reproducing is merely the scolding of dissastisfaction on the part of the speaker who cannot manipulate the youth:

Pity the world, or else this glutton be/To eat the world's due, by the grave and thee.

Sonnet V continues the theme of beauty, reflecting that "never-resting time leads summer on" and brings about the age of "winter."  However, even though the youth has aged, in the third quatrain, the speaker states that "summer's distillation [is] left"  and the "substance" of beauty still shines through, the soul of the person is yet beautiful.  This is expressed in the final couplet:

But flowers distill'd, though they wil winter meet,/Leese but their show; their substance still lives sweet.