Halliday & Matthiessen (2014: 521):
Verbs used in reporting statements and questions are often the same as those used in quoting; but there is one significant difference. In quoting, the independent status of the proposition, including its mood, is preserved; hence the speech function is as explicit as in the ‘original’. In reporting, on the other hand, the speech function is, or may be, obscured, and is therefore made explicit in the reporting verb.