People will realize that he is a prophet. This can be stated in active form. AT: "people will know that you are a prophet" (See: [[rc://en/ta/man/translate/figs-activepassive]])
This idiom means "go ahead of the Lord" or "come before the Lord" (See: [[rc://en/ta/man/translate/figs-idiom]])
# to prepare his paths
This is a metaphor that means that John will prepare the people to listen to and believe the Lord's message. (See: [[rc://en/ta/man/translate/figs-metaphor]])
# to give knowledge of salvation ... by the forgiveness of their sins
The phrase "give knowledge" is a metaphor for teaching. The abstract nouns "salvation" and "forgiveness" can be expressed with the verbs "save" and "forgive." AT: "to teach his people salvation through the forgiveness of their sins" or "to teach his people how God saves people by forgiving their sins" (See: [[rc://en/ta/man/translate/figs-metonymy]]and [[rc://en/ta/man/translate/figs-abstractnouns]])