outspoken: bold; vocal; vociferous
plain-spoken: straightforward; open & sincere; using simple, direct language
unspoken: not said; silent
The above traits of speech may be taken at times as good or bad, deserving respect or annoying. One will probably appreciate someone who is outspoken for his side, but not so if on the other side. To be plain-spoken, straightforward & sincere, might be generally looked on as a good thing -- unless someone is sincerely telling us something we don't want to hear. Some people we had rather be seen and not heard, yet we can still be annoyed by someone's silence.
In God's work we ought to be bold, outspoken, but surely some people are just loud and obnoxious. In God's work we ought to be straightforward & sincere, plain-spoken, using simple direct language. A little tact may not hurt, but we should say what we believe plainly so that in the end everyone understands where we stand and what we believe. We shouldn't be silent, unspoken, about the good news. But we can also learn that we don't have to express our opinions about everything. We don't have to tell everything we know -- some things are better unexpressed (swift to hear; slow to speak).