Many versions understand "light" here to stand for life. That is, the servant will become alive again. (See: [[rc://en/ta/man/translate/figs-metaphor]])
The word "bear" means carry. Possible meanings are 1) "their iniquities" is a metonym representing the punishment for their sins. AT: "he will take their punishment" or "he will be punished for their sins" (See: [[rc://en/ta/man/translate/figs-metaphor]])or 2) "their iniquities" is a metonym representing their guilt. AT: "he will take their guilt upon himself" or "he will be guilty for their sins"