All the Dwarves that were part of the expedition swore an oath to the Earth Goddess, who they worshiped.
This was the greatest oath a Dwarf could make. Even the Dwarfs in Solais shared the same mentality. Once they made an oath, they had to do it no matter what. Failure to do so would weigh terribly in their conscience because it would mean that once they died, their souls would be cast away, forever banished from the Earth Mother's embrace.
"Keep your word, Half-Elf, or I swear by the Earth Goddess that you will not keep your life," Nevreal said in a threatening tone.
"We'll see whose oath will be broken first," Lux replied with a calm expression on his face. "Now, listen to me. Our first goal is to eliminate the guards as fast as we can and prevent alarming the kobolds inside the nest."