Following his time in Morayshire, Morison went further into the Highlands, to Tain, at the request of Presbytery of Elgin to serve its station there for two months (December 1839 and January 1840). A chapel had been built there four months previously. On arrival, he discovered that the Secession influence was minimal, with about sixty people on average attending the services. According to the biographer, Morison brought about a great change in the attitude of the community, with young men being forced to think seriously, some professors of religion realised that they were not possessers of it, and several infidels abandoned their unbelief and became eagers spreaders of the faith. Many came to him for personal counselling. Despite this enlarged interest, little is said in the biography of permanent growth of the Secession church in Tain. Perhaps these converts remained with the Church of Scotland and would have joined the Free Church in 1843.
Morison's preaching and its results inevitably led to several calls from Secession congregations. In March 1840, he preached for the first time in Clerk's Lane Church, Kilmarnock (the congregation in which he eventually became a pastor). Prior to receiving its call, he had thought of becoming a travelling evangelist because of the clear influence his preaching was having on hearers all over the country (including his own family). Generally it was his emphasis on God's universal love that enabled listeners to sense inner peace. This developing situation led him to write his first public tract in which he explained his methods for dealing with those who had spiritual perplexities caused by lack of assurance. He was aware that some of his comments would offend the more conservative ministers of his denomination.
At that time, Morison held to what his biographer calls 'Moderate Calvinism' in which he believed that the atonement of Christ was universal. He realised that this belief had implications for the meaning of the doctrine of election. After some thought, he found an answer in the order of events in God's eternal decree, in which his election of some sinners comes after his decision to provide a universal atonement for all sinners. His biographer does not indicate whether or not Morison asked the obvious question, 'If God planned a universal atonement, why did he not also arrange a universal election?' His attempt to harmonise a universal atonement with a limited election only creates more problems and does not provide a satisfying answer, and Morison himself later realised this was the case.
The congregation in Kilmarnock had begun in 1777 and had enjoyed notable ministries. However, the pastor who immediately preceded Morison had been forced to resign because of his inability to please two opposing groups within the congregation. One group was nominal and the other was evangelical. Their building could hold 1,000 listeners. A listener of Morison's first sermon prior to receiving the call stated that the address gave him 'a marvellous and blissful relief from the doubts which filled my mind by the Calvinistic notions I had received from the Shorter Catechism and the preaching I heard on Sundays'. This individual became a close friend of Morison's. Evidently, even as a probationer seeking a call, Morison made no attempt to hide his differences with Scottish Calvinism.
When the call was signed, it was clear that the congregation was divided, with a substantial group opposed to Morison. Yet the eagerness with which his supporters desired his ministry led him to accept the call. Before he could be inducted, he faced presbytery trials on September 1st, 1840. The demands of the trial were great, but they also revealed Morison's abilities. He had to give a lecture on 1 Peter 1:6-9, exegete Philippians 2:5-11, and preach on 1 Timothy 1:5. In addition, he was examined on the Hebrew text of Psalms 141-150, on the Greek New Testament, and on Church History of Britain and Ireland under Cromwell. He also had to deal with the issue of whether or not a sinner can do anything acceptable to God without the influence of the Holy Spirit. Despite his insistence that Christ's death was universal, his trials were unanimously sustained, although he noticed that almost all of the members were initially prejudiced against his views. Perhaps his views were allowed because he said that he held to the opinions of John Brown, a theological professor in the denomination's college.
Morison then had to be ordained. On October 1st, the Presbytery met for the ordination and it quickly became clear that several members were concerned about some of his comments in the tract he had published. His explanation was accepted, although he advised to be more careful in what he said, and also to suppress the circulation of the tract. This Morison agreed to do and the ordination took place.