Mr Willison’s abilities procured him a remarkable prominency in all public discussions regarding church matters in the period in which he lived, especially in the question of patronage, to which he was decidedly hostile. He was, indeed, considered the leader of the party who advocated the right of the people to choose their own pastors agreeably to the settlement of the church at the revolution, in 1689, and was indefatigable in his exertions to restore the exercise of this popular right, which had been overturned by an act of parliament passed in 1712. In these exertions, however, both Mr Willison and his party were unsuccessful till the year 1734, when they were fortunate enough to procure the co-operation of the General Assembly in their views. That body had hitherto strenuously seconded the enforcement of the system of exclusive patronage, but in the year just named it happened to be composed of men who entertained directly opposite sentiments on that subject to those avowed and acted upon by their predecessors;--so opposite, indeed, that they determined, in the following year, 1735, to apply to parliament for a repeal of the patronage act. The known abilities, zeal, and activity of Mr Willison suggested him as one of the fittest persons to proceed to London on this important mission, and he was accordingly appointed, with two other clergymen, Messrs Gordon and Mackintosh, to perform that duty; but the application was unsuccessful.

Mr Willison also distinguished himself by the strenuous efforts he made to keep the peace of the church, by endeavouring to prevent those schisms, and to reconcile those differences, which led to the separation of large bodies of Christians from the established church, and which first began to manifest themselves about this period. His efforts were unsuccessful, but not the less meritorious on that account.

Besides being a popular preacher, Mr Willison was also a popular author, and in the religious world his name, in the latter capacity, still stands, and will long stand, deservedly high. His principal works are, "The Afflicted Man’s Companion," written, as he himself says, with the benevolent intention "that the afflicted may have a book in their houses, and at their bed-sides, as a monitor to preach to them in private, when they are restrained from hearing sermons in public;" and the work is admirably calculated to have the soothing effect intended by its able and amiable author; "The Church’s Danger and Ministers’ Duty;" "A Sacramental Directory;" "A Sacramental Catechism;" "An Example of Plain Catechising;" "The Balm of Gilead;" "Sacramental Meditations;" "Appendix to Sacramental Meditations;" "A Fair and Impartial Testimony;" "Gospel Hymns;" "Popery another Gospel;" and "The Young Communicant’s Catechism." An edition of these very useful and pious works, in one volume, 4to, was published at Aberdeen in 1817.

Mr Willison is described as having been most exemplary in all the relations of life, and singularly faithful and laborious in the discharge of the important duties of his sacred office, especially in visiting and comforting the sick. In this benevolent work he made no distinction between the rich and the poor, or, if he did, it was in favour of the latter. Neither did he confine his exertions in such cases to those of his own persuasion, but with a truly christian liberality of sentiment, readily obeyed the calls of all in affliction, whatever their religious creed might be, who sought his aid.