One aspect of the Italian style was the approach to the setting of words.
Since the turn of the 17th century, Italian composers had become obsessed with giving vivid expression to words, as in the madrigals of Gesualdo and in the first operas, particularly of Monteverdi. This brought a new boldness in the use of striking harmonies and chromaticisms.
Charpentier did not meet Monteverdi, (Monteverdi died the year Charpentier was born!); but he met, and was strongly influenced by one of his disciples, Carissimi. When he returned to Paris, Charpentier took with him the scores of works by Carissimi, much music in his ‘prodigious musical memory’, and the Italian style in his bones.