Stautory is mandatory as per the Law/Regulation. The law/regulation is normally called as statute.Eg: companies act makes it mandatory for all companies to carry out statutory audit etc.,

Whereas Internal Audit is only mandatory for some companies faling under the criteria as prescribed in the companies Act,2013 for others it is discreationary(not compulsory).

Falling are the class of companies for which Internal Audit is mandatory:

According to Rule 13 of The Companies (Accounts) Rules, 2014 following class or classes of companies shall be required to appoint an internal auditor or firm of internal auditors, namely:

(a) every listed company;

(b) every unlisted public company having- (i) paid up share capital of 50 crore rupees or more during the preceding financial year; or (ii) turnover of 200 crore rupees or more during the preceding financial year; or (iii) outstanding loans or borrowings from banks or public financial institutions exceeding 100 crore rupees or more at any point of time during the preceding financial year; or (iv) outstanding deposits of 25 crore rupees or more at any point of time during the preceding financial year; and

(c) every private company having- (i) turnover of 200 crore rupees or more during the preceding financial year; or (ii) outstanding loans or borrowings from banks or public financial institutions exceeding 100 crore rupees or more at any point of time during the preceding financial year:

The rules also provide that every existing company covered under above criteria in Financial Year 2013-14 shall comply with requirements of Section 138 and Rule 13 of Companies (Accounts) Rules, 2014 before 30th September, 2014 (within 6 months of the commencement of Section 138, i.e. 01st April, 2014).  

There are many advanatges of being  a CA namely :

• you can do own practise
• you can be an employee in an organisation
• you can be an enterpreneur
• you can be journalism
• you can teach

All these are you choice and depends upon your capability.In addition you can command respect in society