Rationalization is the most general element in Weber's theory. It is associated with the attempt to come to a logical and meaningful interpretation of the universe by intellectuals, religious teachers and prophets, and empirical scientists. It is synonymous with the creation of means-ends chains of some sort (or the stripping away of the space between means and ends).
For Weber, the salvation religions have played a key role in the progress of rationalization in the world. However, in Catholicism, the means to reach salvation - for example, confession, ritual - are still somewhat enchanted. Protestantism is significantly less enchanted.
Calvinism, for Weber, is the most Protestant (i.e. most rationalized) sect. The Calvinists believe that God doesn't meddle in the world. Further, they think that it is sinful to imagine that you can influence God, so no appeals to God (e.g. "God, if you get me out of this mess, I promise I'll never drink again.") Thus, there are no moments of enchantment, so Calvinism has reached the limits of rationalization.
Calvinists believed in predestination - that whether you were saved or not could not be changed by your actions, it was predetermined.
If it's already determined, why not hedonism?
This seems logical - if I can't do anything about it, why not just do whatever I feel like doing?
But, Weber argues that it worked otherwise for the Calvinists:
Instead, Calvinists understood themselves as the vehicles God made to produce value. That is, they should work for the glory of God. So, the Calvinists, instead of being hedonists, became the working all the time, frugal, dour, never have fun type.
As a result of all their hard work, they made money. Unlike previous people who made money (hedonists?), they could not just enjoy it - they were working in their calling and had to continue. So, they invested their money and did it all over again.
This cycle of work and reinvestment created the first capitalists.
OR, Capitalists were looking some way to account
for their lives - they were ready for an idea system that worked for them..