Sonnet 126 is the last poem in which William Shakespeare addresses his younger lover and so marks the end of the Fair Youth series in the collection first published in 1609.

The sonnet stands out for its tenderness and the gentle tone with which it reminds the young man that even he – beautiful as he is and ever youthful as he may seem – must ultimately be surrendered by nature to all-consuming time, and for the quiet resignation with which it accepts this as the universal and inescapable truth that is all our fate.
Beyond that, the poem is also formally exceptional: consisting as it does of six rhyming couplets, it isn't strictly speaking a sonnet at all, though either Shakespeare himself or somebody else has furnished it with two sets of empty brackets where a sonnet's closing couplet would normally be. And so Sonnet 126 is genuinely unique: there is none other in Shakespeare's canon like it.

Sonnet 125 is the last in this group of three which effectively concludes the series of sonnets that concern themselves with William Shakespeare's love for his young man.

Sonnet 126 also speaks to the Fair Youth directly, but it forms almost a coda, an epilogue so to speak, to the body of poems addressing their relationship.

Here, in Sonnet 125, Shakespeare once more acknowledges that what he has to offer is not status, nobility, riches, or power, but an honest love that comes from the heart: an admiration, respect, and liking for the young nobleman that is not borne out of duty or a desire to manoeuvre himself into a favoured position, but out of a genuine affection, which he senses, and expresses, he receives in return.

Having denied time the power to make his love change in the previous poem, William Shakespeare now with Sonnet 124 turns his attention to politics, statehood, and the fashions of a notoriously fickle society, and further delineates his love for his young man against such other, more trivial, more volatile, much more feeble affections as it may be surrounded by and as it may be finding itself compared to or accused of being.

When Sonnet 123 addressed time itself directly, this sonnet speaks to no-one in particular but makes a general, and even bolder, assertion that his love is unmatched by any other; that it, in itself, is a kingdom, one might say, which does not rise and fall with fortune or the ever-fluid vagaries of opinion and manipulated opportunity but stands strong and singularly tall.