Runes and items created by them (Shield Weapons / Fire Pick / Hell Maw / etc.) all require energy to use or activate. Energy is gained through the creation of runes that are consumed on use or throwing items into lava or fire within 10 Blocks of you. (Note: The closest person to the burning item will receive energy, regardless of who threw the item.)
Different items have different runic value energies. Please see the Tier page for more information on item values. Consuming or incinerating the same item gives diminishing returns; each time you incinerate the same item in a row, the runic energy reward is reduced by a certain percent. The energy reward cannot be reduced below 1. You can reverse the penalty by sacrificing different item types; each time you sacrifice an item of a different type, the penalty for all other item types is reduced.
The cost of using any given rune can vary depending on several factors - the number of blocks modified by a rune, the distance teleported, the tier of the blocks used to create the rune (if it uses tier blocks), etc.