In 1739, on taking the degree of Master of Arts, Blair printed his thesis, "De Fundamentis et Obligatione Legis Naturæ," which contains a brief outline of these moral principles afterwards developed in his sermons, and displays the first dawnings of that virtuous sensibility, by which he was at all periods of his public life so highly distinguished. On the 21st of October, 1741, he was licensed as a preacher by the presbytery of Edinburgh, and soon began, in the usual manner, to exhibit himself occasionally in the pulpit. Heretofore, the only popular style of preaching in Scotland was that of the evangelical party, which consisted chiefly in an impassioned address to the devotional feelings of the audience. The moderate party, who were of course least popular, had neither lost the practice of indulging in tedious theological disquisitions, nor acquired that of expatiating on the moral duties. The sermons of this young licentiate, which presented sound practical doctrines, in a style of language almost unknown in Scotland, struck the minds of the audience as something quite new. In the course of a very few months, his fame had travelled far beyond the bounds of his native city. A sermon which he preached in the West Church, produced an extraordinary impression, and was spoken of in highly favourable terms to the Earl of Leven. His lordship accordingly presented the preacher to the parish church of Colessie in Fife, which happened to be then vacant. He was ordained to this charge, September 23, 1742, but was not long permitted to labour in so confined a scene. In a few months, he was brought forward by his friends as candidate for the second charge of the church of Canongate, which may almost be considered a metropolitan situation. In the popular election which followed, he was successful against a very formidable competitor, Mr Robert Walker, then a favourite preacher. He was inducted to this charge, July 14, 1743, when he had little more than completed his twenty-fifth year. On the occasion of the insurrection of 1745, Blair preached a sermon, in the warmest strain of loyalty to the existing government, and which he afterwards printed. During the eleven years which he spent in the Canongate, his sermons attracted large audiences from the adjoining city, and were alike admired for their eloquence and piety. They were composed with uncommon care; and, occupying a middle place between the dry metaphysical discussion of one class of preachers, and the loose incoherent declamation of the other, they blended together in the happiest manner the light of argument with the warmth of exhortation, and exhibited captivating specimens of what had hitherto been rarely heard in Scotland, the polished, well-compacted, and regular didactic oration.
On the llth of October, 1754, he was called by the town council of Edinburgh to accept of one of the city charges, that of Lady Yester's church, and on the 15th of June, 1758, he was promoted by the same body to the highest situation attainable by a Scottish clergymen, one of the charges of the High Church. This latter removal took place, according to the records of the town-council, "because they had it fully ascertained, that his translation would be highly acceptable to persons of the most distinguished character and eminent rank in this country, who had seats in said church." In truth, this place of worship might have been styled, in the absence of an episcopal system, the metropolitan church of Scotland. In it sat the lords of Session, and all the other great law and state officers, besides the magistrates and council, and a large congregation of the most respectable inhabitants of the town. It might now, therefore, be said, that the eloquence of Blair had at last reached a fit theatre for its display. In the year previous to this last translation, he had been honoured by the university of St Andrews with the degree of D. D. which was then very rare in Scotland.
Hitherto, Blair's attention seems to have been chiefly devoted to his profession.
