I hope this warning way may be of service to them,and help themjchange their habit.请问这里的of当什么讲?

I hope this warning way may be of service to them,and help themjchange their habit.请问这里的of当什么讲?
I hope this warning way may be of service to them,and help themjchange their habit.
请问这里的of当什么讲?

I hope this warning way may be of service to them,and help themjchange their habit.请问这里的of当什么讲?
be of service to 固定短语 对…有用
be of+名词 ＝ be+形容词
eg.be of importance = be important
be of value = be valuable

应该是be of词组。是具有...性质,内容的意思。
跟下面这个句子用法差不多：
Perhaps this book will prove to be of some use to you in your studies.
也许这本书会对你的研究有用处。