As a Roman Catholic priest, Friar Laurence believes in both Providence, the hand of God, and free will. Since the concept of Fate as a determining factor in a person's life, as exists with Calvinisim, is entirely foreign to Catholicism, it is against his vows as a priest to believe in predestination. However, Friar Laurence does recognize the temperament of a person as a strong contributing factor to the actions of a person.
In Act III, Scene 3 of Romeo and Juliet the impulsive Romeo rushes to the Friar's cell again for advice. This time he has slain Tybalt in the streets of Verona after Tybalt slays his friend, Mercutio. In the first four lines, Friar Laurence cries,
Romeo, come forth, come forth, thou fearful man.
Affliction is enamored of thy part,
And thou art wedded to calamity. (3.3.1-4)
Key to understanding the full import of these lines is the fact that (1) Friar Laurence knows Romeo well and is aware of his capricious and impetuous temperament; (2) he also understands the milieu of enemity in which Romeo lives with the feud of the Montagues and the Capulets. So, given the combination of his being married to a foe's daughter and his youth and impulsiveness, Friar Laurence perceives Romeo's chances of escaping disaster as nearly impossible. This is why he use figurative language to express his dread, telling Romeo that metaphorically he is "wedded to calamity."