"I will influence his thinking" or "I will cause him to think differently." Here "spirit" probably refers to his attitude and thoughts, rather than to a spirit being.
"Fall by the sword" is metonymy for being killed. AT: "I will cause him to die by the sword" or "I will cause some men to kill him with a sword" (See: [[rc://en/ta/man/translate/figs-metonymy]])