Thomas More was executed for treason because of a religious dispute. It wasn't heresy, because that is not how the English Reformation played out. Specifically, More could not acknowledge that Henry VIII was the Supreme Head of the Church of England. He could take an oath acknowledging Henry's temporal power, or he could never have been the Lord High Chancellor of England. Still, it was Henry's desire to annul his first marriage to Catherine of Aragon and remarry to Anne Boleyn. After the Pope did not grant Henry's wishes, Henry listened to reformers and split from the Catholic Church. Although More was a reformer and humanist, he could not countenance this break from the Papacy. Initially, it seemed fine for More simply to resign his post as Lord High Chancellor. Yet his many enemies came after him, and More could not under good conscience say that the crown was the head of the Church in England. He tried to use legal reasoning to say he wasn't actively committing treason for never outright denying Henry's status as head of the Church of England. So he was found guilty of treason, and sentenced to be executed.