Witherspoon's Calvinism as causal leverage for a robust view of rhetoric

Jeffry Morrison in his book, John Witherspoon and the Founding of the American Republic, gives the following evaluation of Witherspoon's view of Church and State:

But for all of his recommendations that magistrates "use their authority for the glory of God" and "reform and restrain impiety," Witherspoon was no theocrat. Nor does his talk of making "public provision for the worship of God" prove that he advocated "active state support of Protestant Christianity," as one commentatory has claimed, let alone any sort of establishment, as others have claimed. To begin with the obvious, Witherspoon did not stipulate "Protestant Christianity,"only public worship that was agreeable to the "great body of the people." Presumably this could have meant the Roman Catholicism in the case of Maryland, a historically Catholic colony, or other traditions at more local levels such as counties or townships. Furthermore, "public provision for the worship of God" could admit of any number of government actions, all short of promoting Protestantism or any sectarian version of Christianity whatever. (34)

How is it that Witherspoon could, as a Calvinist of impeachable Reformed orthodox credentials, advocate for the support of public religion without advocating for establishment? How could such general affirmation be strong enough, explicit enough to ensure that the Christian religion flourish in the way that Witherspoon sought for it to flourish? There is a clue to his confidence in one of his Thanksgiving addresses:

Good laws may hold the rotten bark some longer together, but in a little time all laws must give way to the tide of popular opinion, and be laid prostrate under universal practice. Hence it clearly follows, that the teachers and rulers of every religious denomination are bound mutually to each other, and to the whole society, to watch over the manners of their several members. (23)

It would seem that Witherspoon places the chief burden of securing Christian society, not upon the explicit formulation of laws, but upon the cultivation of Christianity's own citizens by the sound shepherding of her clergy. Establishment by law is of no import should the minds and desires of the people drift away from religious beliefs and practices. Establishment laws may not positively motivate so much as they would constrain certain negative motives popularly acknowledged. Yet should the tide of belief change, the laws (within a republican form of government) would soon follow, or become a dead letter.

Morrison appears to concur, saying, "True religion was to act as a sort of leaven, working its healthy influence throughout the political body without benefit of formal establishment but with equal aid and protection from the state" (36).

Liberty of conscience is the key principle behind Witherspoon's claims, both in ecclesiastical and political realms. If Calvinists would not stand for a Pope or a Patriarch to command their consciences before Almighty God in matters of religion, how could they consistently command such from others where the power of the majority and control of the State was theirs? Within this Calvinist conception of the liberty of conscience lay the seedbed for a robust appreciation for the potentiality, nay the necessity of persuasion, and hence, the necessities of a well-developed theory and practice of rhetoric.