One of the most important part of De Landa’s Relación de las Cosas de Yucatan is the so called “alphabet”, which became fundamental in the understanding and deciphering of Maya writing system.
Thanks to Maya scribes, who were taught and forced to write their language in Latin letters, De Landa recorded a list of Maya glyphs and their corresponding alphabet letter. De Landa was convinced that each glyph corresponded to a letter, like in the Latin alphabet, whereas the scribe was actually representing with Maya signs (glyphs) the sound being pronounced. Only in the 1950s after the phonetic and syllabic component of Maya script was understood by the Russian scholar Yuri Knorozov, and accepted by the Maya scholarly community, did it become clear that De Landa's discovery had paved the way toward the decipherment of Maya writing system.
Sources
Coe, Michael and Mark Van Stone, 2001, Reading the Maya Glyphs, Thames and Hudson
De Landa, Diego [1566], 1978, Yucatan Before and After the Conquest by Friar Diego de Landa. Translated and with noted by William Gates. Dover Publications, New York.
Grube, Nikolai (Ed.), 2001, Maya. Divine Kings of the Rain Forest, Konemann, Cologne, Germany