"I have developed a highly formalised compositional system, which I have been using to write my music for twenty years. Summa is the most strict and enigmatic work in this series", said Arvo Pärt in 1994. The neutral title itself embodies the essence of the content as the work is based on the text of the Latin Credo. The great simplicity of the piece masks its complexity. The underlying rules ensure that on the surface a cycle of continuous change is created while the deep structure possesses an order of stillness.