« REX SEMPITERNE CAELITUM. — Hymn of Matins during the Easter season, by an unknown author of the fifth century, clearly imitating Ambrosian hymnody.
The seventeenth-century correctors substantially revised II. The chant is addressed to Christ, eternal king and creator of all things, who in Adam fashioned man in his own image and likeness and, after the sin, redeemed him by assuming his form and, through Baptism, saved him after having redeemed him. The Cross and the Blood of Christ impart to Baptism its divine power and its fruitfulness.
BIBL.: G. S. Piment, Les hymnes du Bréviaire romain, III, Paris 1884, pp. 93–100; C. Albin, La poésie du Bréviaire, Lyon n. d., pp. 176–80; A. Mirra, Gli inni del Breviario romano, Naples 1947, pp. 116–18.