Dell's 1646 sermon to the lower house in Parliament, following a controversial one to the House of Lords, was too extreme, and the House of Commons reprimanded him; it attacked the Westminster Assembly, spoke up for the poor, and told the politicians to keep out of religious reform. Nonetheless his appointment at Caius was at the behest of the Rump Parliament. Thomas Harrison's proposal to have him preach again, in 1653, was defeated. He criticized those on the Parliamentarian side who had done well out of the war. According to Christopher Hill He backed the Quaker John Crook as MP in 1653/4, and the regicide John Okey. He was a supporter of Oliver Cromwell. In 1657, however, he with Okey campaigned against the proposal to make Cromwell king.
Theology
He was a friend and supporter of John Bunyan, whom he invited to preach in his parish church. He was an opponent of the Ranters; but also of enforced uniformity of worship, citing Martin Luther against it He was attacked as a libertine, and thought to tend to antinomianism. According to Christopher Hill He preached the doctrine of free grace, and subscribed to the idea of continuous revelation; and is included in those considered preachers of the Everlasting Gospel.
Institutions
He argued for major institutional change. He attacked academic education frontally. He proposed a secular and decentralized university system; with local village schools, and grammar schools in larger places. He was strongly against the Aristotelian tradition persisting in the universities, and discounted all classical learning; and expressed broad anti-intellectual attitudes. He believed in more practical studies; more particularly, he was concerned that training for the ministry should be much more widely spread, geographically and socially, and less dependent on traditional academic studies. He was a severe critic of the Church of England. He doubted the basis in scripture for a national Church, and eventually was buried outside it. He had egalitarian views on the suitable social composition of the bishops, and clergy in general. He connected this to religious control and change. Christopher Hill writes He was against monarchy and tithes, with views close to the Levellers.
He was deprived of his living of Yelden in 1662; he had held it from 1642. A 1667 pamphlet of his, The Increase of Popery in England, was suppressed and appeared only in 1681; Hill calls this anti-Catholic attack 'partly a political gambit'
