relying on the work of internal auditors

See the 2nd to last point here:
A7. Objectivity refers to the ability to perform those tasks without allowing bias, conflict of interest or undue influence of others to override professional judgments. Factors that may affect the external auditor’s evaluation include the following:
? Whether the organizational status of the internal audit function, including the function’s
authority and accountability, supports the ability of the function to be free from bias, conflict of
interest or undue influence of others to override professional judgments. For example,
whether the internal audit function reports to those charged with governance or an officer with
appropriate authority, or if the function reports to management, whether it has direct access
to those charged with governance.
? Whether the internal audit function is free of any conflicting responsibilities, for example,
having managerial or operational duties or responsibilities that are outside of the internal
audit function.
? Whether those charged with governance oversee employment decisions related to the
internal audit function, for example, determining the appropriate remuneration policy.
? Whether there are any constraints or restrictions placed on the internal audit function by
management or those charged with governance, for example, in communicating the internal
audit function’s findings to the external auditor.
? Whether the internal auditors are members of relevant professional bodies and their
memberships obligate their compliance with relevant professional standards relating to
objectivity, or whether their internal policies achieve the same objectives.

Aha! I thought I might whet your appetite with that. It’s a copy and paste from the ISA.

You can download the 2018 Handbook Vol 1 pdf from this page: https://www.iaasb.org/publications/2018-handbook-international-quality-control-auditing-review-other-assurance-and-related-services-26
FOR FREE with simple registration here

All the IAASB examinable documents are current in this volume except ISA 315
which is also available for free: https://www.iaasb.org/publications/isa-315-revised-2019-identifying-and-assessing-risks-material-misstatement

I don’t recommend AT ALL that you try to “learn the ISAs” – because they are only relevant to the extent that they have something to say about the learning outcomes that make up the study guide as published in the syllabus.

I do, however, think they are a useful reference especially if you are thinking about doing AAA 🙂

ISAs are generally structured:
Scope – short and generally obvious from the title of the ISA
Effective date – irrelevant
Objective – short and generally obvious
Definitions – a useful reference – but note that there is also a comprehensive glossary at the beginning of the book
REQUIREMENTS – this it the important bit – what the auditor must do
Application and Other Explanatory Material – additional detail (like that which I copied in the post above) that you can dip into.

If you look at ISA 500 – for example – the entire ISA excluding the Application and Other Explanatory Material is less than 3 pages. So far easier to digest than IFRS Standards.