"your shearers are working" or "your shearers have sheep to shear." David wants his men to speak so that Nabal understands that his sheep were well because David's men helped guard them.
David is pointing out how he and his men offered protection to Nabal's servants and flocks. This can be stated in positive form. Alternate translation: "we kept them and all their property from harm" (See: [[rc://en/ta/man/translate/figs-litotes]])