You can't get anything done in life if folks don't believe what you say. Every life relationship is built on trust, including the relationship a trial lawyer has with their jury. Working to convince twelve people to believe you . . . the criminal defense lawyer . . . is a tough, uphill battle. When a prosecutor declares they represent the State, they immediately have credibility with the jury by default. They can lose this credibility, but they usually don't need to work hard to get it. Not so with the defense lawyer. We must earn the trust of the jury. When we stand up to speak people are always skeptical of us and what we have to say.
Moreover, if we want clients to invest in our skills as a criminal attorney, we must prove we are credible and worthy of their trust. When working with prosecutors and witnesses, they must trust us to tell the truth and keep our word. Finally, when in trial the jury must recognize our credibility if they are going to be open minded about our theory of the case. From the moment we walk in, we must appeal to people's logic and reason as well as to their emotion. But first we must convince them we are credible.
In law - as well as in life - credibility is everything. Before establishing any kind of relationship - be that with a jury, a coworker, or a friend - you must first establish trust. In order to be trusted you must be credible. If a criminal defense lawyer doesn't have credibility he has no foundation upon which to build trust. Credibility, therefore, is everything.