Answer:
seriousness
Step-by-step explanation:
The oxymoron is a literary device that is used when two opposite words are put next to eachother, in order to create a certain feeling, a paradox is a statement that contradicts itself, in this case Friar Laurence is telling Romeo and Juliet that they have to love eachother moderately if they want their love to last, since violent consuming lovers often do not last.