Ong published a lengthy review essay about that book and McLuhan's years at SLU in CRITICISM: A QUARTERLY FOR LITERATURE AND THE ARTS (1970). Ong's review essay is reprinted in AN ONG READER: CHALLENGES FOR FURTHER INQUIRY (2002, pages 69-77).
Over his long and productive scholarly life, Ong maintained his interest in Hopkins by occasionally publishing reviews of books about Hopkins and occasionally discussing Hopkins in his own articles. For example, in "Evolution, Myth, and Poetic Vision" in the journal COMPARATIVE LITERATURE STUDIES (1966), Ong discusses Hopkins' poetry extensively. Ong reprinted it in his book IN THE HUMAN GRAIN: FURTHER EXPLORATIONS OF CONTEMPORARY CULTURE (1967, pages 99-126). However, Ong does not mention "Evolution, Myth, and Poetic Vision" in HOPKINS, THE SELF, AND GOD (1986).
Ong's laser-like focus of certain issues in HOPKINS, THE SELF, AND GOD leads him not to mention certain other of his own scholarly publications -- for example, his publications about Milton.
Because Hopkins' poetry was not published until 1918, it was often considered to be part of the literary movement known as modernism. T.S. Eliot and Ezra Pound (1885-1972) were other poets in that literary movement. As a result of that misclassification of Hopkins' poetry, later literary scholars have labored diligently to show that Hopkins should be considered to be a Victorian. In his book HOPKINS, THE SELF, AND GOD, Ong accepts that later literary scholarship and also makes his own contributions to why Hopkins should be considered to be a Victorian.
Ong liked to say that we need both closeness (proximity) and distance to understand something. In HOPKINS, THE SELF, AND GOD (1986), Ong claims that "the technologies of writing, print, and computers" are distancing and objectivizing. He also claims that the "inward turn of consciousness develops in counterbalance with the outward turning implemented by the distancing or 'objectivizing of [those technologies]" (page 130).
Now, Hopkins wrote certain sonnets expressing extremely anguishing experiences. Ong suggests that Hopkins wrote those poems "in part to distance the experience out of which they grew" (page 135). Ong further suggests that writing those poems expressing his extreme anguish may have helped "Hopkins manage the experience better" (page 135).
For Hopkins, I would say that writing those poems about his extreme anguish also involved a kind of self-giving -- a giving of his experiences of extreme anguish to others who might read those poems. Citing Mariani, Ong notes that "such self-giving calls for strong ego-structures" (page 39).
In HOPKINS, THE SELF, AND GOD (1986), Ong discusses energy-center imagery in Hopkins' and other Victorians' writings (pages 17-18, 110-112, and 129).
Even though I do not agree with all of Ong's religious convictions, I stand in awe of his own energy as manifested not only in this book but in his entire body of scholarly work.
After HOPKINS, THE SELF, AND GOD was published, Ong published "Technological Development and Writer-Subject-Reader Immediacies" in the book ORAL AND WRITTEN COMMUNICATION: HISTORICAL APPROACHES, edited by Richard Leo Enos (1990, pages 206-215). Ong's essay is centered on Hopkins and his use of newspaper reports that had been telegraphed in to the newspaper. It is reprinted in AN ONG READER: CHALLENGES FOR FURTHER INQUIRY (2002, pages 497-504). That essay continues and further develops Ong's discussion of electric telegraphy and Hopkins' poetry in HOPKINS, THE SELF, AND GOD (1986, pages 48-52).
For a well-researched recent study of Hopkins, see Dennis Sobolev's book THE SPLIT WORLD OF GERARD MANLEY HOPKINS: AN ESSAY IN SEMIOTIC PHENOMENOLOGY (2011).
In his own way, Ong explores semiotic phenomenology in his own work (he repeatedly says that his work is concerned about noetic developments), perhaps most notably in his essay "Voice as Summons for Belief: Literature, Faith, and the Divided Self" in the journal THOUGHT A REVIEW OF CULTURE AND IDEA (1958). Ong's 1958 essay is reprinted in AN ONG READER: CHALLENGES FOR FURTHER INQUIRY (2002, pages 259-275).
For a bibliography of Ong's 400 or so publications, see the late Thomas M. Walsh's bibliography of Ong's publications, including information about reprintings and translations in the book LANGUAGE, CULTURE, AND IDENTITY: THE LEGACY OF WALTER J. ONG, S.J., edited by Sara van den Berg and Walsh (2011, pages 185-245).