As I looked upon the Catholic Encyclopedia entry on "Regeneration," I was fascinated by what I saw. Below I will quote from the entry, but trim it down for brevity and to highlight some key points:
Regeneration is a Biblico-dogmatic term closely connected with the ideas of justification, Divine sonship, and the deification of the soul through grace. Confining ourselves first to the Biblical use of this term, we find regeneration from God used in indissoluble connection with baptism, which St. Paul expressly calls "the laver of regeneration" (Titus 3:5). In His discourse with Nicodemus (John 3:5), the Saviour declares: "Unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God." The idea of "birth from God" enjoys a special favor in the Joannine theology. Outside the Fourth Gospel (Jn 1:12 sq.; 3:5), the Apostle uses the term in a variety of ways, treating "birth of God" as synonymous now with the "doing of justice" (1 John 5:1, 4 sq.), and elsewhere deducing from it a certain "sinlessness" of the just (1 John 3:9; 5:18), which, however, does not necessarily exclude from the state of justification the possibility of sinning. It is true that in all these passages there is no reference to baptism nor is there any reference to a real "regeneration"; nevertheless, "generation from God", like baptismal "regeneration", must be referred to justification as its cause. Both terms effectually refute the Protestant notion that there is in justification not a true annihilation, but merely a covering up of the sins which still continue (covering-up theory), or that the holiness won is simply the imputation of the external holiness of God or Christ (imputation theory).