"In the midst of life we are in death"

Emily Brent is quoting from the Order for the Burial of the Dead in The Book of Common Prayer

The Book of Common Prayer is the book of services and prayers used in the Church of England, originally published in the 1500s.

Title page, Book of Common Prayer, 1662 version, printed 1762
Public DomainTitle page, Book of Common Prayer, 1662 version, printed 1762

When they come to the Grave, while the Body is made ready to be laid into the earth, shall be sung or said,

MAN, that is born of a woman, hath but a short time to live, and is full of misery. He cometh up, and is cut down, like a flower; he fleeth as it were a shadow, and never continueth in one stay. In the midst of life we are in death; of whom may we seek for succour, but of thee, O Lord, who for our sins art justly displeased? Yet, O Lord God most holy, O Lord most mighty, O holy and most merciful Saviour, deliver us not into the bitter pains of eternal death. Thou knowest, Lord, the secrets of our hearts; shut not thy merciful ears to our prayer; but spare us, Lord most holy, O God most mighty, O holy and merciful Saviour, thou most worthy Judge eternal, suffer us not, at our last hour, for any pains of death, to fall from thee.