When you listen to the Dhamma you must open up your heart and compose yourself in the center. Don't try to accumulate what you hear or make a painstaking effort to retain what you hear through memory. Just let the Dhamma flow into your heart as it reveals itself, and keep yourself continuously open to its flow in the present moment. What is ready to be retained will be so, and it will happen of its own accord, not through any determined effort on your part.
Similarly when you expound the Dhamma, you must not force yourself. It should happen on its own accord and should flow spontaneously from the present moment and circumstances. People have different levels of receptive ability, and when you're there at that same level, it just happens, the Dhamma flows. The Buddha had the ability to know people's temperaments and receptive abilities. He used this very same method of spontaneous teaching. It's not that he possessed any special superhuman power to teach, but rather that he was sensitive to the spiritual needs of the people who came to him, and so he taught them accordingly.
~ Ajahn Chah