“Beauty is found in harmony, not in discord; and harmony implies affinities, but these require a refinement of the senses if they are to be perceived. The beautiful harmonies of nature and of art escape those whose senses are dull. The world is then cramped and cruel. Our surroundings provide us with inexhaustible sources of aesthetic pleasure, but men can still move about in the world as if they had no senses or were like brute beasts looking for pleasure in strong and sharp sensations since these are the only ones accessible to them.” 
Maria Montessori developed the sensorial materials in order to help aid the child’s natural tendency to understand and define his physical surroundings. These materials help the child refine his senses so that he might develop a deeper comprehension of and connection to the world around him.
Sensorial exercises exist to help refine the senses. They cover a range of categories including tactile, temperature, weight, stereognostic, olefactory, visual, and auditory. These materials contain internal controls of error so that the child can realize a mistake he has made without any sort of outside intervention. For example, each of the knobbed cylinders fits into an opening specific to its size and none of the other cylinders. “If he mistakes, placing one of the objects in an opening that is small for it, he takes it away, and proceeds to make various trials, seeking the proper opening. If he makes a contrary error, letting the cylinder fall into an opening that is a little too large for it, and then collects all the successive cylinders in openings just a little too large, he will find himself at the last with the big cylinder in his hand while only the smallest opening is empty. The didactic material controls every error. The child proceeds to correct himself, doing this in various ways…There is, therefore, no question here of teaching the child the knowledge of the dimensions, through the medium of these pieces. Neither is it our aim that the child shall know how to use, without an error, the material presented to him thus performing the exercise well.”  It is important that the Montessori teacher present the materials to the child and then allow the materials to teach the child. In this way, the child is taught that he can independently learn from his surroundings without the intervention of authority.
Each of the sensorial materials also completely isolates a single sense so the child can focus all of her attention there. “Another important particular in the technique of sense education lies in isolating the sense, whenever this is possible. So, for example, the exercises on the sense of hearing can be given more successfully in an environment not only of silence, but even of darkness.” We remove visual stimuli from the child’s experience with the sound materials for the same reason that adults sometimes close their eyes when listening intently to music. Focused attention allows for a deeper understanding and appreciation of any subject.
Montessori held the sensorial materials in very high regard, especially in a 3-6 classroom: “…we may say that the training of the senses is a matter of the greatest importance in education. As a matter of fact, we have a two-fold aim in education. One is biological and the other social. The biological objective is to assist the natural development of the individual; the social objective consists in preparing the individual for his environment, and this also embraces professional education, which teaches an individual how to make use of his surroundings. The training of the senses is, in fact, of utmost importance on both counts. The development of the sense actually precedes that of the higher intellectual faculties, and in a child between the ages of three and six it constitutes his formative period.” She goes on to clarify why it is so important to introduce these materials at this age: “If training of this sort is undertaken at an age when the formative period is naturally over, it will be difficult and imperfect. The secret of preparing one for a particular skill consists in utilizing that period of life between the ages of three and six, when there is a natural inclination to perfect one’s senses and movements…The training of the senses must begin in the formative period of life if we wish to perfect them later through education and make use of them in any particular human skill. This is why such training should be begun methodically in childhood and then be continued during the time when an individual is preparing himself through education for the practical life he will have to live.”  By helping the child refine his senses at a time when he is interested and naturally inclined to do so, we help him lay the groundwork for his future endeavors. By introducing a child to Color Box III (in which the child learns to grade colors from lightest to darkest), we may be planting the seeds for a future master artist.
As with all areas in the Montessori classroom, the sensorial materials were created around the needs of the child. The materials were designed to incite a child’s interest and then further his development through their use. A child from three to six years is eager to understand his surroundings. Montessori created the sensorial materials to assist this process by giving the child a more concrete understanding of the various ways we define our physical reality. When the child is presented with the concept of rough and smooth, he then begins to understand that the world around him is made up of a variety of textures, and he can begin to categorize and name these different experiences. This ability allows him to form a strong connection with the world around him. If a child learns that he can understand his world simply by interacting with it, he might just maintain that mentality throughout his life. Montessori describes the importance of developing the child’s ability to become an observer of his world: “The positive sciences advance through observation, and all the discoveries made during the last century and their practical applications, which have done so much to transform the world, have followed along this same road. We should therefore engender this attitude in the oncoming generation, since it is necessary for modern civil life and an indispensable means for continuing the work of human progress…The training of the sense, insofar as it makes a man an observer, not only fulfills the generic function of adapting him to the contemporary mode of civilization, but it also prepares him for the exigencies of life.” 
Traditional education focuses largely on the intellectual development of the individual. While important, sole focus in this area creates a man who is largely disconnected from his external, and therefore internal, environment. “Indeed, when with intellectual culture we believe ourselves to have completed education, we have but made thinkers, whose tendency will be to live without the world. We have not made practical men. If, on the other hand, wishing through education to prepare for practical life, we limit ourselves to exercising the psychomotor phase, we lose sight of the chief end of education, which is to put man in direct communication with the external world.”  By refining the senses of an individual, we increase his capacity to appreciate and enjoy the subtle nuances of his existence. The smaller the details he is able to perceive, the richer and fuller his life becomes.
 The Discovery of the Child, Maria Montessori, Fides Publishers Inc., 1967, pg. 148
 The Discovery of the Child, Maria Montessori, Fides Publishers Inc., 1967, pg 112
 The Montessori Method, Maria Montessori, Schocken Books, Inc., 1964, pg. 170
 The Montessori Method, Maria Montessori, Schocken Books, Inc., 1964, pg. 179
 The Discovery of the Child, Maria Montessori, Fides Publishers Inc., 1967, pg 143
 The Discovery of the Child, Maria Montessori, Fides Publishers Inc., 1967 pg 146
 The Discovery of the Child, Maria Montessori, Fides Publishers Inc., 1967, pg 145
 The Montessori Method, Maria Montessori, Schocken Books, Inc., 1964, pg. 223