In the nineth century, the Byzantine Empire organised several diplomatic missions in order to include in its cultural commonwealth people who lived close to the its borders. Between those, Cyril's mission among the Slavs was particularly noted. Although the activities of Constantine-Cyril had religious and political character, in general, his mission in the Slavic world was based on an enlightenment and had a deep educational dimension. The aim of this paper is to present the main philosophic ideas of Constantine-Cyril about the role of the knowledge in the life of man and about the importance of education in the mother tongue. Also, in the paper will be stressed that, according to Cyril's philosophy, the education presents power which lies in the zenith of cultural development of the humanity in whole, and because of that, it dislikes borders.