The subject doesn’t matter for the content. For example when he paints the interior of a church, that has nothing to do with any religious beliefs. He eventually sees the environment as meaningless, the absurd value of an image built out of shapes, materials and optic effects as reflections, shadows, colored light, etc. The eventual goal: a strong, catchy image.
Maris is fascinated by how meaningless shapes when coherent to each other, can form a familiar whole. By what happens when an image is converted into a painting, which is different from the original because everything is expressed in paint. He strives to reach the biggest visual effect possible with limited instruments. To him it’s all about the tension between this. The material -paint- has to be clearly visible, but never in cost of the image. The image must be visible through the paint.