User blog comment:Commander VB/Mass Effect 3 story understanding/@comment-5337704-20120824133628

Catalyst was originally designed to broker peace (find a way to allow peace) between the synthetics and organics. Organics were losing, think of the Quarian Geth war. Quarians were losing, and most likely would be removed from the galaxy by there own doing.

Catalyst, however, was designed with a button needed to be pushed to activate it: I.e. the keepers had to push the button, Saren had to push the button, most likely the first organic race was the one that pushed the button for the catalyst to actually do the action. The catalyst decided was the best course of action was to make organics into a synthetic hybrid to keep them from being destroyed, either by themselves or by the synthetics they created. After the cycle is complete, the catalyst turns off. Soverign was left behind (atleast it was this time) wait out till the next organic apex to activate the keepers to activate the catalyst.

Organics figured out the cruicible was a way to get organics to negotiate with the catalyst. No other organics before achieved such a feat. This cycle accomlished it, it is unclear if the crucible itself allowed to alter its programming, or that the logic of the AI broke down because its programming didnt think orgranics could accomplish it.

In either case, the catalyst now relizes that this generation of organics was strong/intelligent enough that they could control or destroy or live in harmony with their synthetic creations (basically however you dealt with the quarian geth war) without being killed off by the synthetics they created. This cycle was the first to unite as a whole and accomplish the grand project.

This is of course my understanding with the limited feedback from the game itself.