# For this purpose

"For this" or "For this reason"

# I was appointed a herald and an apostle

This can be stated in active form. Alternate translation: "Christ appointed me to be a herald and an apostle" or "Christ made me a preacher and an apostle" (See: [[rc://en/ta/man/jit/figs-activepassive]])

# a herald

"an official messenger." A herald is an official messenger who is sent to bring news. 

# I am telling the truth, I am not lying

With these two comments Paul emphasizes that he is telling the truth when he says that he was appointed to be a herald, an apostle, and a teacher. Some translators may prefer to put these comments at the end of the verse.

# in faith and truth

This probably refers to what Paul was to teach about. He may be using "faith" and truth" to express one idea. Alternate translation: "about the message of faith and truth" or "about the true faith" (See: [[rc://en/ta/man/jit/figs-hendiadys]])

