From John Keats' narrative poem:
St. Agnes' Eve—Ah, bitter chill it was!
The owl, for all his feathers, was a-cold;
The hare limp'd trembling through the frozen grass,
And silent was the flock in woolly fold:
Numb were the Beadsman's fingers, while he told
His rosary, and while his frosted breath,
Like pious incense from a censer old,
Seem'd taking flight for heaven, without a death,
Past the sweet Virgin's picture, while his prayer he saith.
His prayer he saith, this patient, holy man;
Then takes his lamp, and riseth from his knees,
And back returneth, meagre, barefoot, wan,
Along the chapel aisle by slow degrees:
The sculptur'd dead, on each side, seem to freeze,
Emprison'd in black, purgatorial rails:
Knights, ladies, praying in dumb orat'ries,
He passeth by; and his weak spirit fails
To think how they may ache in icy hoods and mails.
Tennyson* also wrote a poem on the eve, the vigil of the feast of St. Agnes, virgin and martyr, as this site describes.
The tradition on the Eve of St. Agnes for a young woman to seek a vision of her future husband is explained here:
St. Agnes, like St. Valentine, St. Catherine of Alexandria, and St. Anthony of Padua, is invoked by single women in search of a husband -- and today is a good day to pray such a prayer. In fact, Medieval folklore says that on St. Agnes Eve, girls are often granted visions of their future husbands. Scottish girls would meet in a crop field at midnight, throw grain onto the soil, and pray:
Agnes sweet and Agnes fair,
Hither, hither, now repair;
Bonny Agnes, let me see
The lad who is to marry me.
In some places, it was said that those who fast, keep silence, and conduct certain rituals will have a vision of their future husband. The rituals vary from place to place, but included among them are walking backwards to bed while not looking behind you; pulling out a row of pins, saying a Pater for each one; eating a yolkless boiled egg with salt filling the cavity where the yolk had been, thereby prompting the future husband to bring the girl water in a dream; making a special cake called a "dumb cake," walking backward with it to bed, and eating it; and sprinkling sprigs of thyme and rosemary with holy water, placing them on each side of the bed, and invoking St. Agnes.
*St. Agnes' Eve
by Alfred Tennyson
Deep on the convent-roof the snows
Are sparkling to the moon:
My breath to heaven like vapour goes:
May my soul follow soon!
The shadows of the convent-towers
Slant down the snowy sward,
Still creeping with the creeping hours
That lead me to my Lord:
Make Thou my spirit pure and clear
As are the frosty skies,
Or this first snowdrop of the year
That in my bosom lies.
As these white robes are soil'd and dark,
To yonder shining ground;
As this pale taper's earthly spark,
To yonder argent round;
So shows my soul before the Lamb,
My spirit before Thee;
So in mine earthly house I am,
To that I hope to be.
Break up the heavens, O Lord! and far,
Thro' all yon starlight keen,
Draw me, thy bride, a glittering star,
In raiment white and clean.
He lifts me to the golden doors;
The flashes come and go;
All heaven bursts her starry floors,
And strows her lights below,
And deepens on and up! the gates
Roll back, and far within
For me the Heavenly Bridegroom waits,
To make me pure of sin.
The sabbaths of Eternity,
One sabbath deep and wide--
A light upon the shining sea--
The bridegroom with his bride!