Disclaimer: I do not claim to have any clue about India. I am answering this question because the question says "what do these lines mean", rather than "are these lines an accurate portrayal of what actually happened?".
The lines you are quoting are assuming that Hindus and Muslims are not "natural" enemies. History has examples of how groups that are enemies today might get along better tomorrow, and vice versa. You might take e.g. Protestants and Catholics in most of Europe in the 17th century vs today as an example for the first, and e.g. Poles and Jews in the 16th century vs. the 19th century as an example for the second (though I am just guessing a bit re. Poles and Jews).
Furthermore, the whole concept of Hindus and Muslims as a coherent group, as natural as it may seem, is not a given. Chinese would never sort themselves along lines such as Daoists vs. Buddhists*. The idea of an exclusively Catholic political party would be ridiculous in today's Germany, yet one such party played an important role in pre-Nazi Germany.
What is more, the emergence of such groups can be influenced by outside events. E.g. in the early 1920s, Austrians thought of themselves as part of a German nation and there actually was a strong movement to form a single state. Today this view is an absolute fringe position. There was not much of a shared identity between what later become East Germany in the 1930s, but today there is.
What these lines are saying is that
- (the emergence of) the belief that Muslims and Hindus are groups that are separate from each other, and rather incompatible, was influenced by class interests (in the European context one might think of how rural East Elbia was defined and kept alive by a certain social class), group interests (e.g. every time that protestants somewhere appealed to their protestant brothers) and interests of the political elites (in the European context, I believe Henry VIIIs role in establishing protestantism in England may be the most poignant among many examples)
- some people where actively working to create a stronger sense of identity and coherence among India's Muslims and India's Hindus, either in order to oppose the British or in order to support their respective religious group against the other group. Again for a Non-Indian example, you might think of the role catholicism and a catholic pope played in 1980s Poland. Or of the Jihads that regularly get declared against Western powers. An Indian example that came to my mind may be the role lard and tallow played in the Indian Rebellion of 1857.
- this led to conflicts increasingly being interpreted as Muslims vs. Hindus, and these conflicts tended to lead to communal violence. Analogies from other parts of the world might be how the Northern Ireland conflict is being interpreted as Protestant vs. Catholic, although everywhere else in Europe, Protestants and Catholics get along fine. Or how the Israel/Palestine conflict is interpreted as conflict between Jews and Muslims, even though there are Muslims living peacefully in Israel and Jews living peacefully in certain Muslim countries.
Quite often there is not the one single reason for a violent conflict. This applies to economic or social (a.k.a. "class") differences, religious differences, and a number of other differences you might think of. On the other hand there are conflicts were religion clearly plays a major role (say, the Khajirite uprising in the 7th century). In any case it is usually a good idea to not accept some simple explanation at face value, be it religion, or nationality, class, or machinations of some political elite.
Finally, I think an early example of the view that religious differences might not really matter that much, even if they have grave and important consequences today, is Jonathan's Swift's text about eggs and endianness from 1726.
Since other users seem to care a lot about Marxism, it may be worth pointing out that one good example of "the creation or development of communal consciousness [as] an instrument of struggle" might be the Chinese cultural revolution. Where previously and afterwards students and teachers got along just like everywhere else in the world, i.e. not in perfect harmony, but not killing each other either, in 1966 Mao began emphasizing how China's youth is the vanguard of the revolution and how authority figures are always holding them back.
Thus we have a moment in which group interests (those of students not always in perfect harmony with their teachers)** came together with the interests of a certain part of the political elite (Mao and some allies) to form a group consciousness among much of China's youth (first sentence). The whole point of the exercise was of course a power struggle at the top of the CCP (second sentence). Consequently, a wide range of very normal teacher/student conflicts were reframed as "reactionary teacher vs. progressive student", and regularly taken as a reason to commit violence (third sentence).
On the other hand there of course can be conflicts along community lines without any influence from political elites or from any colonial politics. A typical example might be conflicts between settled and nomadic groups, whjch very easily arise from a direct competition for natural resources. You can find hints of this rather early in the bible (the murder of Abel) and lots and lots of examples from written history.
*though it should be noted that neither Daoism nor Buddhism have the "you shall have no other god beside me" that Abrahamitic religions such as Islam have. I.e. there are many people who may be both Buddhist and Daoist at the same time.
**high school students tend to think they have an interest in schools being closed (at least for a while), in a break from ordinary school routine, and in getting rid of teachers they do not like.