The first sermon he preached in Glasgow, a few months before his settlement as minister of the Tron parish, was on behalf of the Society for the Sons and Daughters of the Clergy. The more intellectual part was an exposition of the principles of Christian charity and his views of pauperism, and the more eloquent part was a touching picture of the family of a deceased clergyman, called to tear themselves from all the beauties of their home, when their hearts were overborne with the far darker melancholy of a father torn from their embrace. Dean Ramsay, who heard this sermon, remarked, in his biographical notice of Chalmers to the Royal Society of Edinburgh, that the tears of the father and preacher fell like raindrops on the manuscript, and from many another eye the like tokens of sensibility were seen to flow.
It is of his appearance on this occasion that an elaborate description was given by Mr. J. G. Lockhart in his pseudonymous publication, _Peter's Letters to his Kinsfolk_. It has been reproduced in almost every biography, but the picture is too striking to be wholly left out here. After describing other features of the face, he remarks:--
'The eyes are light in colour, and have a strange, dreamy heaviness that conveys any idea rather than that of dulness, but which contrasts in a wonderful manner with the dazzling, watery glare they exhibit when expanded in their sockets, and illuminated into all their flame and fervour in some moment of high entranced enthusiasm. But the shape of the forehead is perhaps the most singular part of the whole visage; ... it is without exception the most mathematical forehead I ever met with, being far wider across the eyebrows than either Mr. Playfair's or Mr. Leslie's.... Immediately above the extraordinary breadth of this region, in the forehead, there is an arch of imagination carrying out the summit boldly and roundly, in a style to which the heads of very few poets present anything comparable, and over this region again there is a grand apex of high and solemn veneration and love.... Never perhaps did the world possess an orator whose minutest peculiarities of gesture and voice have more power in increasing the effect of what he says.' [The writer then dilates on his defects in gesture and pronunciation, and the disappointment caused by his first utterances.] 'But then, with what tenfold richness does this dim, preliminary curtain make the glories of his eloquence to shine forth, when the heated spirit at length flings from it its chill, confining fetters, and bursts out elate and rejoicing in the full splendour of its disimprisoned wings.... I have heard many men deliver sermons far better arranged in regard to argument, and have heard very many deliver sermons far more uniform in elegance both of conception and of style; but most unquestionably I have never heard, whether in England or in Scotland, or in any other country, any preacher whose eloquence is capable of producing an effect so strong and irresistible as his.'
It was soon after, that on hearing a speech of Chalmers's Lord Jeffrey remarked, 'I know not what it is, but there is something altogether remarkable about that man. It reminds me more of what one reads of as the effect of the eloquence of Demosthenes than anything I ever heard.'
An extraordinary impression was produced by a sermon preached before the Lord High Commissioner, during the proceedings of the Assembly, from the text, 'When I consider Thy heavens, the work of Thy fingers, the moon and the stars, which Thou hast ordained; what is man, that Thou art mindful of him? and the son of man, that Thou visitest him?' There was a reference to the infidel argument that modern astronomy, through the revelation by the telescope of the boundless multitude of worlds existing in the heavens, had shown the earth to be too insignificant a section of God's universe to justify the incarnation and sacrifice of the Son of God. To refute this objection, Chalmers brought forward the not less wonderful discoveries by the microscope of the minuteness of God's works, and the conclusion was irresistibly established that there is 'not one portion of the universe of God too minute for His notice, nor too humble for the visitations of His care.'