A human language is a kind of code. It functions on the basis of words which is unique verbal symbols which correspond to all the objects or ideas which the speakers of that language need to communicate to one another. It also has rules, followed habitually by its speakers, for linking the words of the language together.
Languages in the sense in which we understand them have developed as the common means of communication of large groups of people who habitually communicate with one another and communicate less often with outsiders. A language draws together the people who speak it, and excludes others. The rules for using a language are followed by all members of the linguistic community, for all wish to be understood. Those rules are typically paralleled by other rules or laws, conventions, customs which all also have to follow if they wish to be socially accepted in that particular social and political community. To be able to speak a language is a badge of membership of a community. It ensures acceptance by other members, provided the other rules of the group are also followed.
Language networks minds together. The possession of a common spoken language and even more, the later possession of a common written language enables each member of a community to benefit from the communicated experience of others, so that the mental capacity of each separate individual becomes less important. It enables fellow-members of contemporaneous groups to share information and experience.
Each people speaking a common language developed a collective memory, a common store of cultural experience on which all could draw. Language enabled a community to build up long-term traditions, beliefs and values which differentiated it from other communities.