This work concentrates on the study of the expression hiuotesía in the writings of the Pauline tradition, the only one to use it in all the Holy Scriptures. Though significant works have been written on this matter, our present research frames a study on hiuotesía in the immediate context of Gal 4:1-7 and accompanied by the expression plerôma tou chrónou, as compared with that of Eph 1:3-10 where, stringly, the expression plerôma tõn Kairôn is used. In this comparison lies the originality of the present research. Since each of the texts that employ this term must be seen in it ampler literary context, the first task is to study the structure of each of those contexts. Next, follows the exegetical study of each of them, taking into consideration semantic aspects, especially in their diachronic approach. We thus manage to identify the range of the word hiuotesía and expression plerôma tou chrónou and plerôma tõn Kairôn in each pericope. Analysis and comparison between these two texts of the Pauline tradition show that the dissimilarities between them result from distinct paradigms which, therefore, demand differing theological approaches. In this sense, the author of Eph, by making his own the expressions hiuotesía and plerôma tõn Kairôn, offers, for his part, a new interpretation, differing from what the author of Gal had previously said by using the expressions plerôma tou chrónou and hiuotesía.