McLuhan was clearly aware of the threat of nihilism while still in his twenties.  The world had lost its bearings and the questions were, how did this happen and how were bearings to be regained? His work over the following four decades and more must be understood in this context.

The Cambridge English School, 1938
In view of the generally recognized collapse of serious standards of living, of taste, and of judgment, it has become almost impossible for an individual to find his bearings amidst the hubbub of cheap excitements today. The attainment of genuine critical judgment was never so difficult, or so rare. If in view of this situation alone, the Cambridge English school might easily vindicate its insistence on the rigorous training of sensibility. And literature, properly considered, remains one of the few uncontaminated sources of nutrition for impulse and the education of emotion. With the failure of the external environment to provide such nutrition, or anything except confused sensations, it has become the major instrument of education.

Wyndham Lewis: Lemuel in Lilliput, 1944
The destruction of family life, in theory and in practice, the flight from adulthood, the obliteration of masculine and feminine has all gone ahead — by means of a glorification of those things. Never was sex so much glorified, children and motherhood so idolized and advertised in theory as at this present hour when the arrangements for their internment have been completed.

Network #2¹, 1953
The area of spatial communication is that of politics, business and power. Time is the sphere of language and knowledge. Equilibrium between these interests means social viability. Divorce between them is the breakdown of communication — the jamming of the social network. Nineteenth century development of spatial communication widened the gap between knowledge and power, [between] poetry (all the arts) and politics [&] business. The withdrawal of the arts to an ivory tower and of politics and business to a tower of Babel is the figurative way of citing the current divorce between knowledge and know-how. Irresponsibility and loss of bearings occurred in both domains.

Gerard Manley Hopkins: Victorian Proto-Martyr of the Arts, 1953
“feedback” [ie, dialogue] is necessary for getting bearings. It is perhaps the essential character of the new mass media of communication that no feedback is possible. A person can be a divinity in radio or pictures and yet remain a lonely, isolated private figure with no experience of his audience. Yet this divorce between the artist and the public, seemingly inherent in our new media, is fatal for the arts. It starves them and misguides them. Hopkins was an early victim of this situation, a kind of proto-martyr of the arts. We have not begun to solve or understand the problems that faced him.

Catholic Humanism and Modern Letters, 1954
Today, therefore, when writing, speech, and gesture have all been mechanized, the literary humanist can get his bearings only by going back to pre-literate societies. If we are to defend a civilization built on the written and printed word against the present threat from TV, for example, we must know what we are defending.

New Media in Arts Education, 1956
this break-through from the visual world into the acoustic world seems to be the most revolutionary thing that has occurred in Western culture since the invention of phonetic writing. To understand the human, social, and artistic bearings of this event is indispensable today whether for the teacher or the citizen. Most of the cultural confusion of our world results from this huge shift in the geography of perception and feeling. 

MM to Serge Chermayeff Dec 19, 1960²
Today, when all of the senses have been externalized [and] the human sensorium is itself a global envelope, it is not only the mix of sense components which is altered, but the total environment of sense has become potentially integral but actually alien and disruptive. My own suggestion is that we are helpless as long as we imagine that it is by some control of programming and “content” that we can make sense of the whole situation. (…) One peculiarity of center-margin relationships is that when freedom of interplay between these areas breaks down in any kind of structure, the tendency is for the center to impose itself upon the margin. In the field of attention which we call perception, when the center enlarges and the margin diminishes beyond a certain point, we are in that induced state called hypnosis. The dialogue has ended. Apropos of “the problem of keeping the capsule’s inhabitants human” — for the capsule there can be no margin. Or rather let us consider that for the capsule the problem is the creation of margin that there may be dialogue.

MM to Jackie Tyrwhitt, December 23, 1960, Letters 277–278³
Now that by electricity we have externalized all of our senses, we are in the desperate position of not having any sensus communis. Prior to electricity, the city was the sensus communis for such specialized and externalized senses as technology had developed. From Aristotle onward, the traditional function of the sensus communis is to translate each sense into the other senses, so that a unified, integral image is offered at all times to the mind. The city performs that function for the scattered and distracted senses, and spaces and times, of agrarian cultures. Today with electronics we have discovered that we live in a global village and the job is to create a global city, as center for the village margins. The parameters of this task are by no means positional [ie, they “are by no means” spatial problems, to be conquered or otherwise politically ‘managed’].

Canadian Poetry, 1965
Canadian landscapes, if used as equations for inner mental states, would yield some quite amazing results. [But] Canadians could never bring themselves to accept the logic of their landscape (…) Had Canadians been daring enough to accept their landscape as the formula for mental states, they would have been projected into non-human orbits at once. (…) This theme of stark isolation and human insignificance (…) was to be repeated by Canadian poet and novelist [over and over again, but without drawing its implications]. What Pascal had shuddered at in the unsocial spaces of the heavens, the Canadian writer lived with at home. 

A Glimpse of Christmas Future (1967)
A satellite environment where the Christmas star that guides us might well be man-made. 

Through the Vanishing Point (The Emperor’s New Clothes), 1968
The artist puts on the distortion of sensory life produced by new environmental programming and creates artistic antidotes to correct the sensory derangement brought by the new form. In social terms the artist can be regarded as a navigator who gives adequate compass bearings despite magnetic deflection of the needle by changing environmental forces. So understood, the artist is not a peddler of new ideals or lofty experiences. He is the indispensable [navigational] aid to action and reflection alike.

MM to Ted Carpenter, April 9, 1969⁴
From Cliché to Archetype is a paradox from beginning to end. It is the clichés that are alive and the archetypes that are dead.  

Take Today, 1972
the new frontier is as invisible as a radio wave. There are no tracks to identify or to locate the new frontiersman, even nostalgically. He has neither retrospect nor prospect in his instant space-time field.  (…) The new frontier is pure opacity.