Sonnet VIII (8)

Music to hear, why hear'st thou music sadly? 

Sweets with sweets war not, joy delights in joy.
Why lov'st thou that which thou receiv'st not gladly,
Or else receiv'st with pleasure thine annoy? 
If the true concord of well-tuned sounds, 
By unions married, do offend thine ear, 
They do but sweetly chide thee, who confounds
In singleness the parts that thou shouldst bear. 
Mark how one string, sweet husband to another, 
Strikes each in each by mutual ordering, 
Resembling sire and child and happy mother 
Who all in one, one pleasing note do sing: 
    Whose speechless song, being many, seeming one,
    Sings this to thee: 'Thou single wilt prove none.'

Music to hear (1): An address to his dear friend: O you, whom it is music to hear.

Sweets with sweets war not (2): you are sweet, thus you should delight in things that are also sweet (i.e. music).

Why lovest thou...annoy (3-4): why do you not gladly love the music you hear; or do you receive some gratification from your boredom ('annoy')?

concord (5): harmony.

unions (6): harmonious chords.

chide (7): scold. The notes rebuke the young friend for not participating in life's harmony by remaining single. 

confounds (7): destroys.

In singleness...bear (8): by remaining a childless bachelor, the friend is failing to play his part in the harmony of life, which is family.

thou single wilt prove none (14): you will amount to nothing by remaining single. Most editors reference Dowden's annotation noting that the line is an allusion to the common saying "one is no number" (see also Sonnet CXXXVI)