Why is Paris at Friar Lawrence's cell at the beginning of Act IV?

In the play "Romeo and Juliet" by William Shakespeare, the Friar (Friar Laurence) is often blamed by audiences and critics for his "meddling" and interference. His outlook,however, on Romeo and Juliet's quandary is different from ours. Presumably, being a man of cloth, or a man of God, his driving motive in life is the promotion of good and the prevention of sin, So when he sees Paris looming in on his cell, he sees sin coming - trouble with a capital T. Because, you see, for Juliet to go ahead and marry Paris would now be bigamy and a dreadful sin at the time because of what the Friar has already done in marrying her to Romeo. He must act quicky and think fast if he is to avert mortal sin, as Paris has come to him to arrange the wedding.