The so-called great undertaking is "meritorious achievement." It is the act of establishing order within one’s own heart, aligning one's soul with the heavens and earth, and forcing the cosmos to shift according to one's own will.
Such cultivation is the means by which Dao Fetus Heavenly Monarchs—those beyond the Golden Core—expand their Dao Hearts and the true intent of the Great Dao. Only through such grand, world-altering achievements can these already immortal deities and spirits advance further.
Faced with an opportunity to create such a great achievement, no intelligent being can resist the temptation.
Chapter 857