The central idea of the passage can be best summarized as:

Directions: The passage below is followed by a question based on its content. Answer the question on the basis of what is stated or implied in the passage.

PASSAGE – II
A community or a social group sustains itself through continuous self-renewal, and this renewal takes place by means of the educational growth of the immature members of a group. By various agencies, unintentional and designed, a society transforms uninitiated and seemingly alien beings into robust trustees of its own resources and ideals.  Education is thus a fostering, a nurturing, a cultivating and a process. Etymologically, the word education means just a process of bringing up. When we have the outcome of the process in mind, we speak of education as shaping, forming, moulding activity - that is, a shaping into the standard form of social activity. 
Since what is required is a transformation of the quality of experience, till it partakes in the interests, purposes, and ideas current in the social group, the problem is evidently not one of mere physical forming. Things  can be physically  transported in space; they may be bodily  conveyed. Beliefs  and aspirations cannot be physically extracted and inserted. How then are they communicated? Given the impossibility of direct contagion or literal inculcation, our problem is to discover the method by which the young assimilate the point of view of the old, or the older bring the young into like-mindedness with themselves. The answer, in general formulation, is: by means of the action of the environment in calling out certain responses. The required beliefs cannot be hammered in; the needed attitudes cannot be plastered on. But the particular medium in which an individual exists leads him to see and feel one thing rather than another; it leads him to have certain plans in order that he may act successfully with others; it strengthens some beliefs and weakens others as a condition of winning the approval of others. Thus it gradually produces in him a certain system of behaviour, a certain disposition of action. The word "environment" denotes something more than surroundings that encompass an individual.
They denote the specific continuity of the surroundings with his active tendencies. An inanimate being is, of course, continuous with its surroundings; but the environing circumstances do not, save metaphorically, constitute an environment. For, the inorganic being is not concerned with the influences that affect it. On the other hand, some things that are remote in space and time from a living creature, especially a human creature, may form his environment even more truly than some of the things close to him. The things with which a man varies are his genuine environment. Thus the activities of the astronomer vary with the stars. Of his immediate surroundings, his telescope is most intimately his environment. The environment of an antiquarian, as an antiquarian, consists of the remote epoch of human life with which he is concerned with, and the relics, inscriptions, etc., by which he establishes connections with that period.
In brief, the environment consists of those conditions that promote or hinder, stimulate or inhibit the characteristic activities of a living being. Water is the environment of a fish because it is necessary to the fish's activities - to its life.
The North Pole is a significant element in the environment of an arctic explorer, whether he succeeds in reaching it or not, because it defines his activities, makes them what they distinctively are. Just because life signifies not bare passive existence, but a way of acting; environment or medium signifies what enters into this activity as a sustaining or frustrating condition.