In 1834, Morison started training for the ministry in Edinburgh at the divinity hall of the United Secession Church, under John Brown, DD (1784–1858).
On 29 September, his ordination day by Kilmarnock presbytery, two members with objections to Morison's views halted the proceedings.
However, Morison's allowed the reprinting of his offending tract by Thomas William Baxter Aveling, a congregational minister in London.
His father, who shared his views, was suspended in May 1842; and in May 1843 there were further suspensions of Alexander Gumming Rutherford of Falkirk, and John Guthrie of Kendal.
Their movement was reinforced by the expulsion (1 May 1844) of nine students from the theological academy of the congregationalists at Glasgow, under Ralph Wardlaw DD; and by the disownment (1845) of nine congregational churches holding similar views.
From the 'relief church' in 1844 John Hamilton of Lauder joined the movement; as did William Scott in June 1845, on his expulsion from Free St Mark's, Glasgow.
His personal influence and that of his writings extended much beyond the community which he headed, and, in a way nonetheless effective because steady and quiet, did much to widen the outlook of Scottish theology.
Always a hard student, he had especially mastered the expository literature of the New Testament; and his permanent reputation as a writer will rest on his own commentaries, which are admirable alike for their compact presentation of the fruits of 'ample learning, and for the discriminating judgment of his own exegesis.
The 'evangelical union', which has been termed 'a successful experiment in heresy', now numbers between ninety and one hundred churches, adhering to the well-marked lines of evangelical opinion laid down by its founder.
Morison's original church removed from Clerk's Lane to Winton Place, Kilmarnock, in 1860; the old building was sold to a dissentient minority which left the 'evangelical union' in 1885.