Michael Cook notes that denial that Jesus died follows the Christian heresy of Docetism, who were "disturbed by that God should have died", but that this concern conflicts with another Islamic doctrine, that Jesus was a man, not God. Quranic commentators seem to have concluded the denial of the crucifixion of Jesus by following material interpreted in Tafsir that relied upon extra-biblical Judeo-Christian sources, with the earliest textual evidence having originated from a non-Muslim source; a misreading of the Christian writings of John of Damascus regarding the literal understandings of Docetism (exegetical doctrine describing spiritual and physical realities of Jesus as understood by men in logical terms) as opposed to their figurative explanations. John of Damascus highlighted the Quran's assertion that the Jews did not crucify Jesus being very different from saying that Jesus was not crucified, explaining that it is the varied Quranic exegetes in Tafsir, and not the Quran itself, that denies the crucifixion, further stating that the message in the 4:157 verse simply affirms the historicity of the event.