1 What is your substance, whereof are you made,
What is your essence, what materials compose you, what are you made of, really, what is your substance 'Substance' = essence, material composition; the beloved's inner being is the question's target.
2 That millions of strange shadows on you tend?
That millions of strange shadows follow you? that so many copies trail in your wake? with infinite imitations 'Shadows' = mere copies, imitations; the beloved casts so much influence that others become secondary reflections.
3 Since every one, hath every one, one shade,
Since each being casts but one shadow, because normally each thing has only one shadow, everyone else has one shadow 'Shade' = shadow; the logic is cosmological: each being should cast only one shadow. The beloved is exceptional.
4 And you but one, can every shadow lend:
Yet you, being but one, project every shadow, but you're one person yet cast infinite copies, you cast all shadows Paradox: the beloved is singular yet infinite; they contain and project all possible forms of beauty.
5 Describe Adonis and the counterfeit,
Describe Adonis—and the copy describe the beautiful Adonis, and his imitation, Adonis and his fake 'Counterfeit' = forgery; the implication is that attempts to depict Adonis are merely shadows of you.
6 Is poorly imitated after you,
Is poorly imitated in comparison to you, is just a pale copy of you, is poorly copied from you Even the archetypal beautiful boy (Adonis) is inferior to the beloved; the mythical original is secondary to the actual person.
7 On Helen’s cheek all art of beauty set,
On Helen's face all the art of beauty sits, Helen's face contains all artistic beauty, Helen with all beauty's art 'All art of beauty' = the perfection of painting and sculpture; Helen is the Renaissance standard of female beauty.
8 And you in Grecian tires are painted new:
And you are Helen painted fresh in Greek garments, and you're Helen redone, perfected, in Greek clothes, you're Helen remade 'Grecian tires' = Greek garments/adornments; you surpass even Helen by being Helen remade, perfected.
Volta The volta shifts from praising the beloved as embodiment of universal beauty to the revelation that what truly matters is their constancy and inner worth, which surpasses all external comparisons.
9 Speak of the spring, and foison of the year,
Speak of spring and the abundance of the year, talk about spring and the year's fullness, spring and all plenty 'Foison' = abundance, harvest; spring and plenty are nature's supreme gifts.
10 The one doth shadow of your beauty show,
The one is merely a shadow of your beauty, spring is just a shadow of how beautiful you are, just shadows of your beauty Even nature's most beautiful season is a shadow, a copy, of the beloved's radiance.
11 The other as your bounty doth appear,
The other appears as your generosity, abundance is just your generosity made visible, plenty reflects your gift 'Your bounty' = your abundance, generosity; the beloved embodies giving itself.
12 And you in every blessed shape we know.
And you embody every sacred form we know. and you contain every blessed form of beauty, you are every blessed form The beloved is not limited to one form; they contain all forms of beauty, sacred and natural.
13 In all external grace you have some part,
In all external beauty you share some part, every kind of outward beauty is partly you, you're part of all grace 'External grace' = outward attractiveness; the beloved participates in all forms of visible beauty.
14 But you like none, none you for constant heart.
But you are like none; none match you for faithful heart. but you're incomparable—no one else has your loyal heart. no one has your constant heart The couplet's revelation: external beauty can be compared and categorized, but inner constancy—faithful love—is absolutely singular and incomparable.