Being swept away represents being destroyed. This can be stated in active form. Alternate translation: "His army will completely destroy a great army as a flood destroys everything in its path" (See: [[rc://en/ta/man/translate/figs-activepassive]] and [[rc://en/ta/man/translate/figs-simile]])
This can be stated in active form. Alternate translation: "He will destroy that army and the leader of the covenant" (See: [[rc://en/ta/man/translate/figs-activepassive]])
"the leader of the priests." This phrase refers to the person who filled the most important religious position that God required in his covenant, that of the high priest.