Rory refers to Pius XI’s encyclical which instituted this feast in 1925. More info at this link. Rory also mentions the Vatican II Decree Ad Gentes. Read at this link. And this great quotation from Lumen Gentium 31: “But the laity, by their very vocation, seek the kingdom of God by engaging in temporal affairs and by ordering them according to the plan of God. They live in the world, that is, in each and in all of the secular professions and occupations.”