Sometimes it can be by chance, almost an accident.
Take the greatest Anglo-Saxon poem, for example, Beowulf. It's well known now - there have been films, and several translations into modern English, including a rather wonderful one by Seamus Heaney the poet. For centuries, though, the poem was unknown, hidden away in a manuscript called the Nowell Codex - which was the only copy in existence. Even that was almost destroyed in a fire - in which case the poem would have been lost forever. Although we say now that this was one of the crowning glories of Anglo-Saxon literature, we don't really know - because we don't know what has been lost. It might have been head and shoulders above all other poems of the Anglo-Saxon period, or it could have been fairly run of the mill, while they thought some other poem was far superior.
Or take the Revelations of Divine Love by Dame Julian of Norwich. This is a masterpiece of medieval writing, the first book in English by a woman, and a meditation on the visions Dame Julian had of Christ which prompted her to become an anchoress, shut away from the world for the rest of her life so she could think about what had happened to her and make sense of it. When Henry VIII suppressed the monasteries, Benedictine nuns from nearby Carrow Abbey took their manuscript with them into exile, and although it was first published in 1670, it was little known until an edition in 1901 brought it to greater prominence. Now St Julian's church in Norwich (almost completely rebuilt after being bombed during the Second World War) is a place of pilgrimage, and there is even a modern Julian Order of monks and nuns in the United States, living according to her teachings.
Thomas Traherne, a seventeenth century mystic, clergyman and poet, was completely unknown to the wider world until some of his private papers were discovered on a bookstall in 1896, after having been hidden away in a private collection in Ledbury, Herefordshire, for almost 200 years. He was rector of Credenhill, near Hereford, for some time. Now there is a chapel dedicated to him in Hereford Cathedral, with some wonderful modern stained glass windows, and he is venerated as an Anglican saint.
And yesterday I was talking to a lady whose great grandfather almost singlehandedly saved much of Breton culture which was in danger of being lost forever. He and a musician friend walked all across Brittany, collecting stories and music from the traditional performers. It would have been at about the same time that people like Cecil Sharp and Vaughn Williams were collecting English folk songs before they were lost forever.
The lady I was speaking to has friends who are actors, and she asked one of them if he would perform some of the Breton poems for a video she wanted to make. The actor she asked couldn't do it, but suggested someone who could - and while he was reading through the poems she showed him, he came across one that surprised him. It was in Breton and French translations, but it concerned a saint and a holy well on an island near Anglesey in North Wales. It turned out that the lady's great grandfather had spent some time in North Wales, and while there he had come across the poem in Welsh and translated it into Breton and French. Since then, it had been completely lost in Welsh - but now a lady in Anglesey has translated it back into Welsh from the Breton and French versions.
St Dwynwen became a hermit on Llanddwyn Island (which is named after her). She was one of the many daughters of King Brychan - nearly all of his many children became Welsh saints - and retreated to her hermitage after refusing the hand of a young man called Maelon in marriage. Her feast day is 25th January, and she is the Welsh St Valentine, being the patron saint of lovers (and also sick animals!).
The lady I was speaking to had visited her holy well on the island, and tidied up the rubbish around it when she was there. Then she took a photo from the nearby hill - and when she showed it to people, there was a sunburst of light she hadn't noticed at the time, coming off the sea in the background. The locals were in no doubt - this was a sign of great favour from the saint, who had marked the lady for one of her own.