People who accurately convey the content of scripture are not trying "to speak for God", though. They are simply following his word - and his law.
True, but be careful not to be citing one verse and ignoring others. For instance, John 3:15-18 says:
“The Son of Man must be lifted up, that everyone who believes in him may have eternal life. For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. For God did not send his Son into the world to condemn the world, but to save the world through him. Whoever believes in him is not condemned, but whoever does not believe stands condemned already because he has not believed in the name of God's one and only Son.”
Which would indicate 'once saved, always saved' and the only way to lose salvation is to willfully renounce God. Reconciling all the verses of the Bible takes serious study and thought, and people who throw out one verse often don't get the entire message.