Kennedy was devoted to the Presbyterian cause in Scotland against the efforts of King Charles I to impose an Anglican form of church polity on the northern kingdom in 1638.
After the defeat of the Covenanters at the Battle of Kilsyth in 1645, Cassilis fled to Ireland, but in the next year was one of the Scottish commissioners who met with King Charles to gain his assent to the decisions of the English (Puritan) Parliament.
[10] Aware that Charles was having difficulty solidifying support in England, Cassilis and two other commissioners, acting through the Prince of Orange, sought to put his mind at rest: If in any particular our answers be not fully satisfactory to his Majesty's desires, we humbly conceive it more expedient that his Majesty, putting himself on the affections of his [Scottish] people, should refer them to his [Scottish] Parliament where his Royal presence will obtain more than we are warranted to grant,[11]Charles, despite a few more attempts at negotiation, assented to this proposal, though historian Samuel Rawson Gardiner has noted that behind the scenes "the Duke of Lorraine, the Queen of Sweden, and the Prince of Orange .
Scottish historian George Buchanan summarized the planks of the Test Act by pointing out that those who wished to hold office had to swear the following: .
that they owned and sincerely professed the true protestant religion contained in the aforesaid confession of faith; that they believed it to be founded on and agreeable to the written word of God; that they would adhere to it all the days of their lives, educate their children therein, and never consent to any change or alteration contrary thereunto.
In this summary, the duty of associating together, of resisting tyranny, and limiting the power of the magistrate is expressly asserted as a sacred obligation; but without adverting to that circumstance, the test oath in the next sentence affirmed that the king’s majesty was the only supreme governor of the realm over all persons and in all causes civil or ecclesiastical; and the lieges swore that they would never consent or determine upon any subject relating to the church or state without his express permission; that they held it unlawful to form associations for redressing grievances or to take up arms against the king; that they would never decline his power and jurisdiction in any case, but would defend the same against all deadly; and this oath was required to be taken in the plain genuine sense of the words, without any equivocation, under the penalty of confiscation.
[16]That the king's legitimate children and brother were to be exempted from the Test Act became a sore point among the Scots, and reaction was so extreme that the Marquess of Argyll and others elected to leave the kingdom rather than submit.
[17] Tensions continued to mount, and the Covenanters took to the hills, where they would worship in secret meetings, called conventicles, to avoid punishment.
However, to demand conformity, the Duke of Lauderdale pushed through the Conventicles Act in 1670 with penalties so severe—not stopping at execution—that even the king stated he would not have passed it had he known all ramifications.
[18][19] In 1675, despite the fact that all Scottish nobles and landed gentry were forbidden to leave Scotland, Cassilis was the first to exit, making for London to complain to the king about Lauderdale's severe measures.
Regarding the response of the king, David Hume wrote, "These violent proceedings of Lauderdale were opposite to the natural temper of Charles and he immediately issued orders for discontinuing the bonds and the writs of law-burrows,” yet later was heard to say, "I perceive that Lauderdale has been guilty of many bad things against the people of Scotland; but I cannot find that he has acted anything contrary to my interest".
In 1827, Robert Chambers in his Picture of Scotland added the fiction that the Earl imprisoned his wife for the remainder of her life, and that while she still lived, he married another woman.