The book of James is intensely practical. James reminds me of Proverbs. Most of James is not deep theology that is hard to understand, but basic, boot camp material. Some people want to move on to the deeper waters. Practical must mean shallow and not very spiritual, right?
A secret of the wise is that everyone needs the basics, the fundamentals. The so-called deeper material is built on the basics. To swim in the deeps, everything you learned in the shallows has to be second-nature. If you observe athletes in training, you will see them practicing the basics; the simple stuff.
How we listen and how we speak are fundamentals, they are basic building blocks that our Christian lives are built on. If they are faulty, it will negatively effect our lives in Christ.
When we are slow listeners, we are not tuned in to others. We are distracted. We talk back fast. Sometimes we respond back, when the other person has not even finished speaking. We talk past people. This all does not make for good fellowship or community!
When we respond quick and don't hear others, it is a "self" problem. We are selfish and lack self-control. The Spirit of God helps us with self-control. Our self wants center stage in our lives.
When we are selfish and want to be the center it is often linked to low self-esteem. It is like eating candy. It tastes good for a minute, but is not nutritious and does damage. It is a paradox that the egotist and narcissist actually suffer from low self-esteem, a deep sense of inadequacy, and self-hatred.
The person who selfishly talks quick, re-actively, and does not hear others ("I knew what you were going to say"), really has a love problem. They need to receive God's love in their hearts and have that love take hold and bear fruit. The fruit of the Spirit is firstly love, and lastly, self-control (Gal. 5:22-3).
Christian people with good self-esteem, receive God's love, love themselves, and want to love others. Listening is loving and basic. You might have a lot to say in response to someone else. If they can hear you, you will be able to slowly tell them everything in your heart.
Slowly means hesitant, as in when a filter slows down the flow. We sometimes say to someone, "you are too slow"; or of someone, "he is slow to get this". James is saying that we need to be like that with speaking: hesitant and pausing. People who have no self-control and just react will think we are dumb when we are slow to speak. But you are not. You are wise if you slow down your speaking and quicken your hearing.