All items thrown into sacrificial pits are sacrified unless the they have no value, or the item is repairable by sacrificing said item.
To sacrifice an item, throw it into a sacrificial pit. Items thrown in quick succession will be considered part of the same sacrifice, increasing the sacrifice's value. The larger the sacrifice's value, the better rewards a player will receive from the sacrificial pit.
After a player stops throwing items for a few seconds, the sacrificial pit will then return to them their randomized rewards. Additionally, if the sacrifice was valuable enough, the sacrificial pit may award the players with divine blessing in the form of a prayer.
To repair an item via a sacrificial pit, simply throw the item into said sacrificial pit. It will then be returned to you repaired.
Note: Some items (e.g., the Unleashed Sword) require additional items (e.g., Imbued Crystals) in your inventory that are consumed to repair the item.
To check the sacrifice value of an item a player must hold the item, then run the command:
/sacrifice value
Sacrificial pits can be created by players using arranged Chisled Stone Bricks.
The Chisled Stone Bricks must be at least two blocks deep, and must be between twenty-four and four-hundred columns. This means the smallest sacrificial pit possible can be made with fourty-eight Chisled Stone Bricks.
In addition to increasing the value of the inputs to get better rewards, a couple of tomes can be useful.
The Tome of Sacrifice provides direct improvements to the rewards granted by sacrificial pits.
The Tome Of The Cleanly improves rewards for experienced players by removing low value rewards, "cleaning them up."