Sonnet XXII

My glass shall not persuade me I am old,
So long as youth and thou are of one date;
But when in thee time's furrows I behold,
Then look I death my days should expiate.
For all that beauty that doth cover thee,
Is but the seemly raiment of my heart,
Which in thy breast doth live, as thine in me:
How can I then be elder than thou art?
O! therefore, love, be of thyself so wary
As I, not for myself, but for thee will;
Bearing thy heart, which I will keep so chary
As tender nurse her babe from faring ill.
   Presume not on thy heart when mine is slain,
   Thou gav'st me thine not to give back again.

Sonnets 20 - 32 present an ocean of relative tranquility, in which some minor matters of social difference appear to darken the horizon momentarily, and then pass away. Apart from that, the love which has been declared in 13, 15 and 19 But, love, you are etc.; dear my love, you know; 13. And all in war with time for love of you etc.; 15. my love's fair brow; My love shall in my verse ever live young; 19, is allowed to develop to full maturity. In this sonnet it is as if the point of no return has been reached. The expressions of care and tenderness, of love's togetherness and the prospect of youth growing old, of two hearts united in one, of the commitment of love until the severance of death, combine to make this a rare moment in the heart's history. Love triumphs over age and death. Yet in the background there is always the looking in the glass, the reflections in the mirror, so often evoked in these sonnets, which cast back one's own face beated and chopped with tanned antiquity, and the fair youth's face which must go the same way in the end.

There may well be a significance in the number alone of this sonnet, since multiples of 11 seem to exercise some sort of fascination for the writer. Thus 77 and 88 both step aside to look into the future, 66 renounces the world completely, 55 takes a grand and distant view of the passage of time. Although 33, 44 and 99 do not seem to have any special significance, (but see the commentary to 99 for its dating significance), it may be simply that we fail to see it, or that these numbers are not deemed to be as critical as the others and the various climacteric ones, such as 63, 70 and 81.

  Commentators refer us to the traditions of love poetry, in which hearts are interchanged. Sir Philip Sidney's madrigal My true love hath my heart and I have his is the locus classicus of the convention. 

My true love hath my heart and I have his,
By just exchange one for another given.
I hold his dear, and mine he cannot miss:
There was never a better bargain driven.
My true love hath my heart and I have his.

His heart in me, keeps him and me in one.
My heart in him, his thoughts and senses guides;
He loves my heart, for once it was his own:
I cherish his, because in me it bides
My true love hath my heart and I have his.

The Bargain by Sir Philip Sidney 1554-1586.

In this sonnet the convention seems to come of age, for it brings us away from the pastoral and courtly traditions of rarified love and panting swains and suddenly confronts us with the painful responsibilities of loving, the need to care and to protect, the overwhelming sense that everything that you do will have an effect for good or ill upon the loved one, and the tenderness and devotion which are inseparable from it. Lines 9-12 evoke a solicitude which is rare in love poetry anywhere, and the haunting finality of the closing line, which seems to declare that from now on there can be no turning back, 'the bow is bent and drawn, make from the shaft', leaves one with a sense of awe that mortal love can be so absolute and uncompromising.

The 1609 Quarto Version

MY glaſſe fhall not perſwade me I am ould,
So long as youth and thou are of one date,
But when in thee times forrwes I behould,
Then look I death my daies ſhould expiate.
For all that beauty that doth couer thee,
Is but the ſeemely rayment of my heart,
Which in thy breſt doth liue,as thine in me,
How can I then be elder than thou art?
O therefore loue be of thy ſelfe ſo wary,
As I not for my ſelfe,but for thee will,
Bearing thy heart which I will keepe ſo chary
As tender nurſe her babe from faring ill,
   Preſume not on thy heart when mine is ſlaine,
   Thou gau'ſt me thine not to giue backe againe.

Commentary

1. My glass shall not persuade me I am old,
My glass = my mirror. The mirror reflecting back an ageing face should tell the person who looks into it that he is old, as in 62, quoted below. Looking glasses are mentioned in the following sonnets: Look in thy glass and tell the face thou viewest 3; My glass shall not persuade me I am old, 22; But when my glass shows me myself indeed,/ Beated and chopp'd with tann'd antiquity, 62; Thy glass will show thee how thy beauties wear, 77; Look in your glass, and there appears a face/ That over-goes my blunt invention quite, 103; I have not included double references where the word occurs twice in a single sonnet. glass in 5 refers to a glass vial. In 126 I believe it refers to an hour glass.
2. So long as youth and thou are of one date;
are of one date = are both of the same age. youth here must be construed as an abstraction which remains permanently youthful. Each person for a short time is of the same age as youth, until he/she grows on, leaving youth behind.
3. But when in thee time's furrows I behold,
time's furrows = the wrinkles which time creates in the forehead as one ages. They are like the parallel lines or furrows created by the plough in a ploughed field. Cf. 63:
When hours have drain'd his blood and fill'd his brow
With lines and wrinkles
Compare also
O, carve not with thy hours my love's fair brow,
Nor draw no lines there with thine antique pen; 19
4. Then look I death my days should expiate.
Then look I = Then I anticipate that.
should expiate = will bring to an end, to the time when it expires. expiate can also have the meaning of redeem, or do penance for sins. It probably has that secondary meaning here, in the sense of paying one's debt 'to time and mortal custom'.
5. For all that beauty that doth cover thee,
All your beauty. It covers him in the sense that he is entirely beautiful. Or as clothing covers the body. Hence it becomes the raiment of the next line.
6. Is but the seemly raiment of my heart,
seemly raiment = decorous garments, clothing, adornment.
Seemly = suitable, restrained, decorous, in that nothing appertaining to the youth is unfitting.
7. Which in thy breast doth live, as thine in me:
Which - the antecedent is my heart, with a backward look at seemly raiment and all that beauty.
as thine in me = as your heart lives in my breast. Although by now I think it becomes unclear (intentionally so) as to the whereabouts of either's heart or breast.
8. How can I then be elder than thou art?
elder = older. Or perhaps an elder person.
9. O! therefore, love, be of thyself so wary
be of thyself so wary = treat yourself with the like care and concern as I etc.
10. As I, not for myself, but for thee will;
The intermingling of hearts and minds continues. for thee will = will look after myself, for you, since I and you are one.
11. Bearing thy heart, which I will keep so chary
which I will keep so chary = which I will treat with as much care and caution (fearing lest I hurt or damage it). chary is used adverbially. OED.8. gives, alongside this example, one from Marlowe:
Thanks, Mephistophilis, for this sweet book, This will I keep as chary as my life. Faust.vi.175.
12. As tender nurse her babe from faring ill.
This comparison defines wary and chary above.
faring ill = coming to harm. As in the parallel contrary expression to fare well, meaning to come to no harm, which became so common as to be used as a formula at parting.
13. Presume not on thy heart when mine is slain,

Do not assume that when my heart dies, yours will survive. In slain there is a suggestion of the harm that a lover can do.

Kill me with spites, yet we must not be foes. 40
Use power with power, and slay me not by art,139.

14. Thou gav'st me thine not to give back again.
This anticipates 116
Let me not to the marriage of true minds
Admit impediments,
and other sonnets. The giving of love is not a conditional gift.