Why did Piet Mondrian favor vertical and horizontal lines during his Cubist period?

During his Cubist period (1912–1917), Piet Mondrian increasingly favored vertical and horizontal lines as part of a deliberate effort to reduce individual forms to a general formula and move beyond the depiction of specific objects.1

While he initially utilized the Cubist scheme of composition, he sought to push his work toward total abstraction by avoiding diagonal accents and curved lines. This evolution was significantly influenced by his interest in theosophy and his acquaintance with the philosopher M.H.J. Schoenmaekers, whose work on the symbolic meaning of lines and the mathematical construction of the universe provided Mondrian with a formal vocabulary. By using only vertical and horizontal lines, Mondrian aimed to create a "pure" reality and transform the canvas into a site of spiritual awakening, ultimately leading to his signature style of Neoplasticism.123