«O thou, my lovely boy, who in thy power
Dost hold Time’s fickle glass, his sickle, hour».
Sonnet 126 is the last of the poems about the youth, and it sums up the dominant theme: Time destroys both beauty and love.
O thou, my lovely boy, who in thy power
However, the poet suggests that the youth, “Who hast by waning grown and therein show’st / Thy lovers withering as thy sweet self grow’st,” remains beautiful despite having grown older. Because the youth is mortal, he will eventually die, but the poet does not appear to be as concerned with this future event as he was in earlier sonnets. Nor does the poet feel the need to state that the youth will live forever in the poet’s sonnets. He is much more confident that his sonnets will exist forever — and the youth in them — and so does not feel it necessary to bring this to the youth’s attention.
Unlike the previous sonnets, this sonnet consists of twelve lines in rhymed couplets, and it serves as the envoi — a short, closing stanza — of the sonnet sequence dealing with the young man. Now the poet is concerned with the ebb and flow of things, of renewal and degeneration. With this sonnet, the poet comes full circle from the deferential submission in the early sonnets to equality and independence, “poor but free.” That is, he will no longer need to be tactful or guarded in his criticisms of the young man.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com