But in your hearts set apart Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience, so that those who speak maliciously against your good behavior in Christ may be ashamed of their slander. (1 Peter 3:15-16 NIV)
I think this is a scripture that should be a challenge to all Christians. As Christians we tend to miss the mark on this one in one of two ways. One of the ways we can miss this this is to not be ready to answer when people want to know about our beliefs. As Christians it is important that we not just be able to parrot off the doctrinal statement but actually be able to explain it. We don't have to know it all but actually making some effort makes a huge contribution to the credibility and integrity of our message in the eyes of those we tell it to.
On the other hand knowing why they believe what they believe is not a problem for some Christians. It's how they say it that is the problem. Whether it be enthusiasm, arrogance or just bad communication skills, the gospel and Christian viewpoints are often presented in really unhelpful ways. Just as being uninformed can damage our witness, so can our attitude when we present the gospel. Have a bad one and people aren't hearing the message, they're hearing your attitude. If you don't know something they are asking about, swallow your pride and say so. Gentleness and respect are so important.
Personally i need to work on both at times. Sometimes I can be not thoughtful enough. Sometimes I need to work on how i go about talking about what i know. How about you?
I'll leave you will a clip of Mark Driscoll discussing this text.