And now, Lord, look upon their threats and grant to your servants to continue to speak your word with all boldness...
Acts 4:29

Speak the truth in boldness and God will carry your words to their intended ears.

OTOH, that's not an excuse to ignore principles of rhetoric and persuasion! "God helps those who help themselves" isn't in the Bible, but it's still Scriptural. For example, "A gentle answer turns away wrath."