First off, I must reiterate that you, reader, should begin by reading Peter Webster’s summary and overview of MacIntyre’s book.
Once you’re done with Webster, I would recap that, in this book, MacIntyre asks and answers three questions as follows:
Question One (addressed at length in the first post): “[W]hy [has] secularization […] not progressed any further than it has done, especially among the working class”? 
As MacIntyre puts, it, social differentiation from class division has resulted in a social environment where it is impossible for a coherently unified set of aims and needs to produce agreement across them, whether religious or atheistic or even moral; each class has its own morality and aims and needs, often at the expense of the others. Thus,
[t]he dissolution of the moral unity of English society and the rise of new class divisions lead to a situation where […] there remains no framework within which the religious questions can be systematically asked. [29-30]
–or within which “secular” answers can gain a comprehensive foothold. As he sums it up:
the explanation both of the secularization of English society and of the limits to that secularization are to be found in the changes in the value-system of the community, brought about by the Industrial Revolution and by the consequent class division of English society 
With no common set of aims, and very different moral universes, neither Christianity nor Marxism nor some simple form of secularism will present themselves as comprehensive explanations for all of society. At least the U.K. is held together only by the secondary virtues.
Question Two (addressed at length in the second post): Is “religious decline is a, or the, cause of moral decline”? 
The answer: it is neither. Instead, religious decline has followed upon moral decline, and moral decline has resulted from the loss of a shared set of needs and goals between the different classes after first urbanization and then industrialization robbed the classes of a common moral universe. The needs of the classes are too different, and their goals are too different.
Liberalization, or the maximizing of individual autonomy, has resulted in people having a strained relationship even to their class, however. Likewise in the breakdown of those institutions and contexts that were common across classes, like marriage and monogamy and sexual purity, or else national political life being the horizon of political action (gone after WWI). People experience more economic mobility, so they end up moving between classes and erecting a kluge of the different moralities of different classes.
Further, once they were institutionalized, the secondary virtues –tolerance, cooperation, &c.; virtues that don’t tell you how to live but rather how to go about the business of dealing with others who are radically different from you– which were the parking lot virtues of getting along with those one disagrees with both for the sake of commercial prosperity and in order to get any project pushed forward, ended up making the recovery of a real moral community across classes –a community that shares needs and aims– impossible. As MacIntyre sums up:
In so far as there is a causal relationship between morals and religion it has been changes in the moral climate and in the forms of social life that have rendered Christianity apparently irrelevant or incredible, rather than unbelief in Christianity which has produced moral change. 
Question Three (addressed at length in the third post): “[W]hat effect [has] secularization […] had upon English Christianity”?
By secularization MacIntyre simply means “the transition from beliefs and activities and institutions  presupposing beliefs of a traditional Christian kind to beliefs and activities and institutions of an atheistic kind.” [7-8]
The short answer is that it has had an enormous impact by denying Christianity comprehensive explanatory power or power to implement its vision in the wake of class divisions after industrialization’s pluralization, but does not allow an alternative comprehensive vision because of the very same pluralist situation it creates.
The somewhat longer answer: Secularization, under first urbanization and then industrialization, has resulted in class differences that are fundamental in determining the aims and needs of social groups, and this has created different moral universes. This radical class pluralism has forced the churches to respond, on the whole, in one of three ways:
(1) to become a sect, in which it withdraws from claims to be able to address all areas of society (it addresses only the elect — who happen, usually, to be members of only one economic class), and to be able to meet the needs of each and offer justifications for the whole to everyone;
(2) to claim immunity from the current social stratification and differentiation, and to claim that its theology is universally relevant even against the sociological evidence that it cannot address the needs and offer convincing reasons for its policies to some quarters of society or transform the social situation (it can merely declaim from on high — or, more often, from the position of one section or class and its needs; this, at least, has the advantage of being coherent in its theological claims, even though it massively fails in the areas noted); and
(3) liberalization, in which Christian theologians attempt to evacuate the social demands of Christian teaching from concrete contents in order to offer more abstract principles that are felt to be more in keeping with life on the ground, but which end up offering no actual direction or practices by which people might discern the ends they should seek.
In MacIntyre’s account, (3) ends up being very telling, because it shows that we are in the wreckage of Christendom, but that there does not seem to be a way forward to something else, that the real and radical pluralism of the present moment inherits Christian language and responses without being able to convincingly apply them to all class situations, but without another overarching language to replace them with.
There are several reasons MacIntyre offers for this, and they seem almost casually chosen; if one wishes to look at them, one can read the headers for the third lecture/chapter.
I expect I’ll offer some reflections on all of this in the next post.
Header image found here.