The sonnet seems well adapted to expressions of love, adoration, longing and even lust. And for some time, fifty or eighty years after it was introduced from the Italian into English poetry, that was almost its exclusive function. For half a century or so the writing of love sonnets was all the rage among the gentry and courtiers of Elizabeth's court. Then, as with all things, the form which had once seemed so vibrant began to feel trite and formulaic. This was partly due to overuse, and even more due to the weakness of many of the poets who had been using it while it was the rage. So it goes with all fads; they fade.
The sonnet had become the meduim of choice for every half-baked infatuation. It no longer carried the extended passion of a Sidney or a Spencer or a Shakespeare. Poor poets allowed its fire to die down.
And the sonnet slowly fell out of favor.
Then came Milton: the only poet who has ever been a serious contender with Shakespeare for the title of the greatest English poet.
In his hands the sonnet no longer was constrained to be love notes to pass to a pretty maiden at a royal ball. Milton freed the sonnet to almost every use that any other speech may have.
He wrote sonnet tyrades against political rivals, pleas for Cromwell and other Protestant leaders to go to war, and melancholy worries about how little he had accomplished in his long life now that he had reached the advanced age of 23. But mostly his sonnets were to, or in honor of, friends. They give one the feeling that they might have been written on cafe napkins over a cup of coffee and sent home with the friend as a parting gift.
Yet, what must it have seemed like to the first readers of Milton's sonnets to encounter in them political argument and casual thanks to a friend for the memory of hanging out together. It must have made as much sense as finding the same themes in a "Roses are red, violets are blue. . ." verse. Or to find a serious theological argument in a limerick! Such things make no sense to us. So it must have seemed to the first readers of his sonnets.
More than any poet before him Milton adapted the sonnet to general use. Surprisingly it worked! In his hands it worked well.
Consider his most famous sonnet, which blends metaphysics and theology in what was for him a painfully personal contemplation.
ON HIS BLINDNESS
When I consider how my my light is spent,
Ere half my days, in this dark world and wide,
And that one talent which is death to hide,
Lodged with me useless, though my soul more bent
To serve therewith my maker, and present
My true account, lest he returning chide,
'Doth God exact day-labor, light denied,'
I fondly ask; But patience to prevent
That murmur, soon replies, 'God doth not need
Either man's work or his own gifts, who best
Bear his mild yoke, they serve him best, his state
Is kingly. Thousands at his bidding speed
And post o'er land and ocean without rest:
They also serve who only stand and wait.'
And yet, as well as his sonnets work with his varied themes, it is with a feeling of coming home that we find in his last sonnet that he, almost reluctantly, returned the sonnet to the theme of love. This was written very late in his life, after the death of his second wife. Naturally it is not the same youthful giddy infatuation that had killed the sonnet years earlier. This is the love of maturity, the love that knows its beloved.
ON HIS DECEASED WIFE
Methought I saw my late espoused saint
Brought to me like Alcestis from the grave,
Whom Jove's great son to her glad husband gave,
Rescued from death by force though pale and faint.
Mine as whom washed from spot of child-bed taint,
Purification in the old law did save,
And such, as yet once more I trust to have
Full sight of her in heaven without restraint,
Came vested all in white, pure as her mind:
Her face was veiled, yet to my sight,
Love, sweetness, goodness, in her person shined
So clear, as in no face with more delight.
But O as to embrace me she inclined
I waked, she fled, and day brought back my night.