"they will hammer their spears into pruning hooks" or "they will make their spears into tools for caring for plants." A pruning hook is a knife that people use to cut unwanted branches off of plants.
"no nation will lift up its sword against another nation." The sword is a metonym for war. Alternate translation: "one nation will not fight wars against another nation" (See: [[rc://en/ta/man/jit/figs-metonymy]])
"nor will they even train to fight wars." The writer expects his reader to believe that those who fight wars train before they fight and that some who train do not fight.