"Messenger" is a symbol of a messenger of God, a person who speaks on behalf of God, who proclaims the Truth to the nations according to His Will.

"Herald" is a person who leads a righteous life, who faithfully perceives and understands the revelations of God's Covenants, the Commandments, which he preaches to the people.

Negative meaning.

"Herald" is a person who has perverted the spiritually-shaped texts of the Scriptures of the Prophets by literalism of their perception and therefore spreads false knowledge about God, communicates false beliefs, false doctrines.