Question: What is this ___ sutra about?
Answer: While this is a very good question, it is also very difficult to answer simply. It is especially difficult to answer due to the length of the scripture and its many important subjects covered.
The question is as hard to answer as ‘Who are you?’ The way to truly know the sutra to study and contemplate it, followed by cultivating according to it, to realise its truths.
Just as the way to know ‘you’ is to reflect on yourself thoroughly, even a mere summary will never be good enough to do full justice to the sutra. What need is detailed study, with commentary and enquiries if needed, ideally through attending a class guided by a qualified teacher.