As air breathing creatures we are well removed from our natural environment when underwater scuba diving. In order to survive, let alone enjoy such activities we must acquire a range of skills and knowledge that are not part of our normal experience. This is most satisfactorily provided by a qualified scuba instructor. An instructor is some who teaches, informs and directs. Applying this definitions to the diving situation we will begin to understand what is the need of a scuba diving instructor.
In order to conduct a good scuba diving course, it is essential for any scuba diving instructor or dive operators to process high personal skill levels and an extensive diving knowledge in the subject (scuba diving in this case) they are going to teach or impart. Inevitably this will demand an appropriate base of practical experience. Additionally teaching skills as demonstrations, communications and supervisions combined with virtues of patience, sensitivity and caring nature must then be added to these diving skills to produce an effective diving instructor.
Student divers that are trained by a good scuba diving instructor will acquire good diving habits and practices from the beginning, whereas uncorrected bad habits learnt during early training are very difficult to rectify later. Diving related accidents can be traced back to such training and habits, which in turn are the result of poor or inadequate instructions.
Source: https://singaporedivecenter.com/the-scuba-diving-instructor/