The Editor's and the reviewers' comments are as follows:
a very thorough editing is a must
What does the last line mean? What kinds of things do I need to do?
I think I need to check the whole manuscript for finding language problem.
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You're probably correct, the editor is asking you to check the whole manuscript for English. If you have a friend who's fluent at English you can ask him / her, otherwise you can also contact a copyediting service such as Enago or Editage (this is not a recommendation for either service, since I have never used them before).