By advice of Archbishop Spotiswood, Durie had written to Aberdeen divines, seeking their opinion on the points of dispute between the Lutherans and the Reformed.
[2] On 20 February 1637 Sibbald and five other Aberdeen doctors, headed by John Forbes (1593–1648), gave it as their judgment that Lutherans and Reformed agreed in those points on which the ancient church had been of one opinion.
[2] On the arrival in Aberdeen (20 July 1638) of the deputation, charged with the task of procuring adhesion to the "national covenant" of 28 February (drafted by Alexander Henderson, (1583?–1646)), the same six doctors, with the temporising adhesion of William Guild, presented further "demands," questioning the lawfulness of the covenant.
Sibbald returned to Aberdeen in August, and resumed his ministry on 13 October, practically accepting the situation, but resolutely declining to subscribe the "national covenant.
[2] In October he again sailed for England, but returned to Aberdeen at the beginning of 1641, having received no encouragement from the king.
Sybold" who joined (August 1646) in the address to Ormonde, thanking him for "the free exercise of the true reformed religion according to the liturgy and canons of the church," and who signed (9 July 1647) the "declaration" maintaining that the directory was without royal authority, and seeking permission "to use the Book of Common Prayer.
But this term is not inapplicable to Sibbald, a Scottish churchman, strongly attached to primitive doctrine, but accepting the ecclesiastical arrangements made by lawful authority.