Frier lawrence is the priest who Romeo wants to marry him and Juliet.

I think that Frier's role is to marry them, but also be there for both Romeo and Juliet.

"Wisely and slow... They stumble that run fast" could be a warning to Romeo that is he rushes things too fast, bad things might happen.

It would be wise of him to take things slow.

yes...but will he? He's impulsive!

no, he probably won't.