The perception of the external world is dependent on the mind. We cannot find a material world that exists totally separately from the mind. The material world is a reflection of the mind rather than an independently existing thing. If your understanding of this leads you to realise the nature of mind, you will automatically realise the nature of the external world. It is not necessary to separately examine the nature of the world. We realise the nature of the external world through realising the nature of mind because of unity in diversity. This is the same as the realisation of non-dual wisdom.

-- Gampopa