Here the 1907 LDS vest-pocket edition accidentally replaced the singular gerundive ministering with the plural ministerings, perhaps because of the preceding plural revelations or the following angels. Elsewhere the text has two examples of “the ministering of angels” (Jacob 7:17 and Moroni 7:25) but none of “the ministerings of angels”.
Summary: Maintain the singular ministering in Omni 1:25; the text consistently reads “the ministering of angels”.