The Nestorian Breviaries , which have most faithfully preserved the ancient texts , have never been printed .
Manuscripts are rare , while the collections of hymns apart from liturgical books are few and have not been sufficiently studied .
The Nestorian Breviaries , which have most faithfully preserved the ancient texts , have never been printed and manuscripts are rare , while the collections of hymns apart from liturgical books are few and have not been sufficiently studied .