One of the distinct human characteristics is a language. And it is fundamental to the society. Our faith, therefore, is related to it. And James gives a practical guides in our texts, which is be quick to hear, slow to speak and slow to anger. This is not about the speed of our conversation, nor about the skill of it. Instead, it is about our stance (attitude), which can be described as humility. In order for us to be quick to hear and slow to speak and anger, we must admit that our thought - basis of our hearing and speaking - might be wrong. Otherwise, we won't listen, and won't need to slow down before speak.
The reason why we should do it is, first, because we are the servants of Jesus. James as a half brother of Jesus considered himself as a servant (v.1). And he is writing this to his fellow Christians (v.19). Also, we are to do it because it leads us to the righteousness of God, not the anger of man.
How can we be quick to hear, slow to speak and slow to anger? It is possible when we take off what we have inside (filthiness and wickedness) and put on the implanted word with meekness. When God's word come into us, we can listen to it first, before we speak and get angry.