In his view art had the meaning to be a truthful spiritual expression. (tes.com)
Non-objective painting is not simply abstraction by another name, but a distinct movement arisen from the desire to divorce abstract painting from its derivative reliance upon objects in the world, whose mundane existence was considered insufficient for manifestations of spiritual expression. (artsy.net)
By 1958, whatever spiritual expression Rothko meant to portray on canvas, it was growing increasingly darker. (en.wikipedia.org)