Friar Laurence(Lawrence) is angry with Romeo in Act III, Scene 3 because he feels Romeo is being ungrateful, narrow-minded, and irrational. Normally, for killing a man, such as Tybalt, the punishment would be death. However, the prince has seen that it was not entirely Romeo's fault that Tybalt was killed, taken pity on Romeo, and banished him from Verona instead of sentencing him to death. Friar Laurence is also angry at Romeo because he is threatening to commit suicide, which is a grave sin.
Friar Laurence argues that in committing suicide he would lose heaven, earth, and love and he would shame "thy shape, thy love, thy wit." He also argues that in killing himself he would kill Juliet whom he vowed to cherish, committing perjury, or making himself a liar.
He further argues that he has many reasons to be glad and thankful: 1) "Juliet is alive"; 2) Tybalt did not kill him; and 3) He has not been sentenced to death, but exiled instead.
Therefore, Friar Laurence declares that Romeo should stop crying and pouting, stay the night with Juliet, and leave for Mantua first thing in the morning. While Romeo is living in Mantua, Friar Lawrence plans to announce their marriage, put an end to the fight between his family and the Capulets, beg the prince's forgiveness, and then bring Romeo back to Verona.