At the core of Sheppard's continuing concern with legal improvement was the presumption that every man had the right to expect justice to be done. The two compelling forces in his life, the law and religious practice, were both subjected to public scrutiny during the years in which he was approaching his professional maturity. When the heated debates in the Long Parliament gave way to civil war Sheppard, believing that the political changes of his generation brought with them the possibility and even the assurance of improvement, did not hesitate to offer his services to parliament's cause. Several years of active involvement as a county committeeman had brought him into contact with the disruptive activities of radical groups as well as with the disturbing proposals for social change that were being circulated in political and religious pamphlets. Responding to those revolutionary proposals, Sheppard had by the early 1650s written tracts reaffirming his support for the traditional class structure, particularly the professions of the law and of the ministry, and for the protection of property rights. But while he remained a strong advocate of retaining the social cement of law and religion, he continued to publish criticisms of contemporary legal practice, asserting his optimism that improvement was possible and that deficiencies in the legal system could be corrected.

The master design for reform that Sheppard created was commissioned by a head of state in a unique period of English history when the constitutional revolution made it possible to consider carrying out genuine innovations in the very structure of the institutions of law and of government.