In Act II, Scene 3, although the Friar has spent the entire scene outlining reasons why Romeo should slow down with his love, he turns around and...

Although the Friar has raised many objections to Romeo's definition of love, especially because he was able to forget Rosaline (who he claimed to love so much) so quickly and move on to Juliet, he ultimately agrees to marry Romeo and Juliet because he hopes that the alliance between the two young people will lead to an alliance between their two houses.  He says, "In one respect, I'll thy assistant be, / For this alliance may so happy prove / To turn your households' rancor to pure love" (2.3.97-99).  The feud between the Montagues and Capulets is responsible for a great deal of violence in Verona, as we see in the first scene of the first act, and Friar Lawrence is peace-loving.  He hopes that uniting the youngest members of the families in holy matrimony will have a positive effect on the families and finally allow them to put their grudge behind them (to everyone's benefit).