"My paintings are not about what is seen. They are about what is known forever in the mind." - Agnes Martin (From an article by Susan York)
How can the word "forever" be used in connection with the human mind, which is certain to decompose? This gets at Martin's philosophy. It doesn't have to do with the soul's survival after death. It is about the human mind accessing something that is going to last forever. Her paintings attempt to access this something (Truth, as it is traditionally called), or at least to express to the viewer this striving towards Truth. It occurred to me, as I sat for hours in front of one Agnes Martin, that she was expressing the way Truth undergirds all of nature.
These thoughts are notoriously hard to communicate and writings about Truth have been famously misconstrued (to mean exactly the opposite of their intended meaning, in fact). That is probably why Martin was very careful with everything she said in interviews, and often repeated the same statements, or simply rephrased them. Nabokov wrote out everything he said in lectures or interviews beforehand, and Kurt Gödel was similarly reticent (all believers in essentially the same philosophy). So, for fear of making a terrible blunder, I think I'll stop here for now with my philosophy lecture.