But McCahon was also controversial and often misunderstood.
"When the Government of New Zealand presented Australia with a great religious I AM painting the gift aroused controversy on both sides of the Tasman," said McNamara.
"The aspect of his work that puzzled many was the way he used words as part of his painting.
"The words were part of his message about the need for enlightenment and prophecy and the way he painted them was in keeping with his visionary purpose."
In nominating the top 20 New Zealanders of the 20th century the Herald said he "captured the essence of who we are as New Zealanders, one of the most innovative and important painters of religious art in modern times, profoundly influenced by taha Maori".
Further reading:
Biography of Colin McCahon, Te Ara Encyclopedia of New Zealand
'Biography of Colin McCahon', Te Papa Museum of New Zealand
'Colin McCahon', Colin McCahon House online
Further viewing
'Colin McCahon: I Am', Documentary, NZ On Screen, 2004