Sure, you should know the words and say them so they can be understood. But CDs, producers, and audiences are looking for more. If it were only about the words they'd just have Siri do the role for a lot cheaper.
Don't act the words. For example, don't say the line, "I'm worried," showing that you're worried. Find what's really happening. Discover what you want from the other character and how you're using the lines to get that. People generally don't say exactly what they're thinking or feeling. There's something else going on. Sometimes even the opposite of what you're saying.
Have an experience...and let the words ride on that experience!