Being a leader involves bringing people together for a common purpose, so credibility is critical.
Communicating effectively and sincerely opens the door to understanding...allowing people to trust the person in charge and want to follow his or her lead. This is a skill, which for some comes naturally but for most needs to be acquired; and can be mastered using the techniques in "THE LEADER'S GUIDE TO SPEAKING WITH PRESENCE" by author John Baldoni.
You want people to feel comfortable when you are speaking. You want them to pull close to you so they see what kind of a presenter you are.
When you seek to put others at ease, you are taking control of the situation. You are demonstrating a sense of confidence, and when you are feeling confident, you will feel a greater sense of control. You will adopt another persona: ownership of the message. You become the expert and you want to share your expertise with others.
Source: John Baldoni: The Leader's Guide to Speaking with Presence: How to Project Confidence, Conviction, and Authority