J. H. Beadle describes the endowment, and asserts that its penalties were for atoning for sins.
J. H. Beadle, Life in Utah: or the Mysteries and Crimes of Mormonism, Being an Expose of the Secret Rites and Ceremonies of the Latter Day Saints (Philadelphia, Pa.: National Publishing Company, 1870), 494
The candidates then kneel and join a solemn oath, repeating it slowly after Adam: That they will preserve the secret inviolably, under penalty of being brought to the block, and having their blood spilt upon the ground in atonement for their sin;