Who is to lead the transition towards Communism?
Who is to lead the transition towards Communism? How can we achieve Communism if we know that the People are separated by ethnicity, religion, and so on? How does the implementation of Socialism correlate with the Economy and the Society?
I would like to thank you for forwarding those questions, and frankly speaking, I hope that my explanation will be able to cover this topic as a whole and explain it, at least briefly. In the first stages of marxism and its development as a theory, the achieving/implementation of the marxian principles fell to the lot of the proletarians, as a whole mass. Practically, the working class was to be directly responsible of the overthrow of the capitalist exploiters (i.e Bourgeoisie) and the transition to a class-less communist society.
Ofcourse, this had many flaws and thus, it would be hardly to believe that a heterogeneous mass would be able to efficiently lead itself in the struggle against capitalism and achieve Communism. Therefore it was given birth to the idea that a Party, which represents the Vanguard of the Proletarians, is to lead the political struggle of the masses and to lead the transition towards Communism.
"In our opinion, what has been said needs no proof, for it is self-evident that, so long as the capitalist system exists, with its inevitably attendant poverty and backwardness of the masses, the proletariat as a whole cannot rise to the desired level of class consciousness, and, consequently, there must be a group of class-conscious leaders to enlighten the proletarian army in the spirit of socialism, to unite and lead it in its struggle. It is also clear that a party which has set out to lead the fighting proletariat must not be a chance conglomeration of individuals, but a united centralised organisation, so that its activities can be directed according to a single plan." (Stalin)
Having said that, I believe that we have clarified to whom belongs the primary responsibility of safeguarding a Socialist Revolution and transition to Communism.
Nevertheless, moving on to your next question, I would like to mention that every society differs, for that every society has its own ideals, its own culture, opinions, and so on. I will try to explain in a general way the methodology of Marxism and its application in the Society, but ofcourse, you must take into account the fact that this is just a brief explanation and does not correlates totally with the Realities of every Modern Society. One can commit a fallacy if he believes that my following explanations can be applied word-by-word for every Society.
The People from within a Society can be indeed separated by ethnicity, religion, or other factors, and doubtlessly, it is not easy to unite and break the barriers that divide the People. And here comes the role of the Party, which, as a Vanguard of the People, aims to promote class-consciousness, to combat racism, and therefore, to practically educate the masses in such a manner that the once-vaunted barriers that dispersed the People to be nothing but vanquished. Ofcourse, you may aswell ask me how can this be done, and then I'd answer simply by pointing out that educational and social reforms and measures can bring those ideas into reality.
At the same time, we must take into consideration that every individual differs from another, and that the People, as a whole, are a heterogeneous mass. The beliefs and the system of values of an individual do not necessarily constitute a barrier in the path of People's Unity unless those (The Beliefs) are in contradiction with this ideea.
Regarding your question which refers to how exactly will be Economy work, and, practically, what effects will the transition towards Socialism have upon the Society and how it will "remodel" to fit the Socialist Realities.
I would like to say here, that first of all, the elimination of the bourgeoisie will have a considerable impact upon how the Economy will be working. As the class that owns the Means of Production has been eliminated, those are taken by the State, and thus, the State becomes the primary owner of Factories, Industry, etc. Therefore, the People are the one to own the Economic Power of a Country, and not the Bourgeoisie.
Hence the transposition of theory into practice has been made, and several Countries have achieved and experienced Socialism, I will generalize the correlation between Marxism and the Society as the following.
The Society will shift accordingly to the Socialist Realities, thus, the principles that govern the Society which are specifically to the old Bourgeois one, will dissipate or adapt to the Theory of Marxism. At the same time, all branches which are correlated to the Society will suffer some changes, and here, I could give example the Juridical System, for that it will function on a relatively different basis that the Capitalist one.
Comrade, I hope that my answers were of use, although I didn't span towards all of the issues of the topics above