in表示“在（某一方面）”
这个句子中,不宜换成of,可以换成for.
如果是of ,那么writing the passage就会和purpose成为对等关系,即一个purpose.
如：
I came to Brighton for the purpose of seeing you.（我来布莱顿的目的就是见你.）
下面一句用了of,但不会引起混淆.
The purpose of the research is to try and find out more about the causes of the disease.