Friar Laurence provides foreshadowing in the passage from Romeo and Juliet by warning the lovers about the dangerous and potentially destructive nature of their intense passion.
"These violent delights have violent ends" - This line foreshadows the tragic ending of Romeo and Juliet's relationship, as their love will eventually lead to violence and death.
"And in their triumph die, like fire and powder" - The comparison of their love to fire and powder highlights the explosive and unstable nature of their passion, suggesting that it may ultimately lead to their downfall.
Together, these two lines foreshadow the tragedy that will befall Romeo and Juliet, and suggest that their intense love will not have a happy ending.