Blest day of God, most calm, most bright. J. Mason. [Sunday.] First published in his Songs of Praise, 1683, as the second of two hymns entitled "A Song of Praise for the Lord's Day," in 6 stanzas of 8 lines and 1 stanza of 4 lines. Early in the present century centos from this "Song” of various lengths began to be introduced into the hymn-books of the Church of England, and later, into Nonconformists’ hymnals also; but in scarcely a single instance do we find the same arrangement in any three collections. In modern hymnbooks both in Great Britain and America, the same diversity prevails, no editor having yet succeeded in compiling a cento which others could approve and adopt. No collection can be trusted either for text or original sequence of lines. The full Original text, however, is easily attainable in Sedgwick's reprint of the Songs of Praise, 1859. The opening line sometimes reads:—"Blest day of God, how calm, how bright," as in Mrs. Brock's Children's Hymn Book,1881, No. 40, but the use of this form of the text is limited. Taking the centos together, their use is extensive.
-- John Julian, Dictionary of Hymnology (1907)