You can make explicit that Christ must also die. Alternate translation: "that Christ must suffer and die" (See: [[rc://en/ta/man/translate/figs-explicit]])
"he would proclaim the message about the light." To tell people about how God saves people is spoken of as if a person were speaking about the light. Alternate translation: "he would proclaim the message about how God saves people" (See: [[rc://en/ta/man/translate/figs-metaphor]])