Abstract
This article deals with the Latin composition of Dietrich Buxtehude «An filius non est Dei». The amazing harmony, completeness of the figurative content and perfection of the form equates this composition with the Passion cycle «Membra Jesu nostri». In this article the author puts the questions of the music and text-music form. Thus particular attention is devoted to the composer’s method of work at the text. The author tries to find the answer to the question what occurs in music when the composer transforms the poetic text into prosaic and why he does that.