Prayer in all its fullness is nothing else than making oneself open to God. This sounds very simple, but it is hardly an answer to the question ‘What is prayer?’ It is merely the start of the answer. What then is being open to God, and how does one make oneself open to God? Perhaps the best way for us to begin is by our considering the two most fundamental acts that man performs. Because he is man, and not animal, his most fundamental, most characteristic acts spring from his rational nature. Using a form of expression which is not fundamental, but which is nevertheless deep rooted, we say that these two most characteristic activities of man are those of his mind and his heart. With his mind he understands, and with his heart he loves. Being open to God, then, is having one's mind open to God and having one's heart open to God.