What do the signers pledge to do at the end of the Declaration of Independence
They were committing treason by signing that document, and they knew it. They were literally putting their lives and fortunes on the line. Should the revolution fail, or any of the signers be captured by the British, they would very likely be executed. As for pledging their "sacred honor", yes, that's a way of saying I'm "all in" and, more to the point, "I'm not going to betray this (new) nation."