Lux aeterna was commissioned by the 1982 Three Choirs Festival in association with the Arts Council of Great Britain. In composing a work dedicated to his mother, Mathias decided against setting the normal Regquiem text, the concept of ’Light’ meaning more to him that of ’Rest’. The text brings together words from the Requiem mass, the Mass in Ordinary, the Mass for a Woman not a Martyr, and the Vespers for Trinity Sunday - sung in the main by the large choir, four anthems to the Blessed Virgin - given to the boys choir; and on a third level, four of Roy Campbell’s English translations of poems by St John of the Cross - sung by the three soloists.
Formally the work falls into three sections, each part beginning with an increasingly passionate plea for salvation. The work ends with a reiteration of the great prayer for eternal light.