In his introduction to Et Sur La Terre in Maitres de la Gravure: Chagall, Roger Passeron has some interesting comments about André Malraux's Preface to the work:

In 1977, Galerie Maeght produced Et sur la Terre, Andre Malraux’s book on the Spanish Civil War, illustrated with 15 aqautints in black and white by Chagall. The book was published in an edition of 205 copies, numbered 1 to 205 signed on the colophon by Chagall. In a letter Malraux sent Chagall and published by Maeght in April 1977, Malraux, the writer, government minister, and long-time admirer, marveled at the fidelity of and complete rapport of Chagall’s illustrations with his text. He was even more astonished, he said, for in sending the manuscript he expressed his own views and then said, “do what you did with the Dead Souls (1923-27) or the Anti-Memoires (1969).” And then, Malraux went on, he made a few “suggestions’ not just to show him what not to do but what to do! Don’t attach too much importance to the characters, he told Chagall, it’s not necessary to show anything more than shadows. And for the décor, make it a vague hall in a hotel during the war in Spain, with that eerie light during black-outs, the “Prussian blue” blisters, the  streets in Barcelona at night, and for the  towns, “show the abundant vegetation, the sky against the sea, the deep green of the trees.”  In the letter Malraux continued to talk about  what he had expected based on the latest paintings and lithographs of Chagall’s he had seen: he had imagined the illustrations would be filled with the Milky Way, the environment on fire with illusions. Thus his astonishment. He had forgotten that Chagall was a meticulous illustrator, and that he should have understood from his earlier books. The evidence was there, in the work, for each of the books described, underlined the fidelity of Chagall in the rapport of the text of the book and the illustrations of the artist. 

Passeron further comments: But what was the most curious was that a man of the quality of André Malraux, with his formidable  artistic culture, with his close relationships with all the great artists of the twentieth century, Picasso, Masson, Chagall, Braque, Miro, with those who were the most important  to Kahnweiler, could be ignorant of such a fundamental truth: for modern artists , all work commanded within such precise limits appears as a constraint and restricts all liberty of expression. In our time, there is no art without liberty, without liberty the artist becomes a mediocrity, a failure.  Never did Vollard, never did Kahnweiler make such a mistake. At most, they threw out a really vague idea, especially Vollard, and were never astonished by what followed. Chagall followed his own inspiration, without deviating from his habitual method.  We’ve noted elsewhere that these aquatints are the only engravings he made that represent bombers and artillery of modern war. . . .