Reading advise on bicategory theory

Hi, I am looking for advise on suitable litterature for a beginner in bicategory-theory. The litterature I have found so far is: Kelly, Street Review of the elements of 2-categories Borceux Handbook of categorical algebra 1 I have also ordered the following article: Benabou Introduction to bicategories So far I have only read Borceux's book but it contains mainly definitions. In particular I have difficulties understanding the need for (and consequences of) the coherence axioms associated with the natural isomorphisms expressing the associativity and identity 'axioms'. /Lars Lindqvist