It was of course necessary, when he had advanced somewhat in his divinity course, that he should practise the art of composition. His first efforts, we are told, were poor enough. The composition both of his letters and his college exercises was bald, unrelieved by any gleam of fancy or sentiment. But in two years he had learned to write with ease and fluency, and he had formed that remarkable, if somewhat turgid style which he practised ever after. We know so little of the English writers who engaged his attention at this time that the natural history of his style is something of a puzzle. It has somewhat of the swell and dignity of Johnson, and much of the diffuseness of Burke – two of the most prominent writers in his youth. But its main quality must have arisen from the burning fervour of his own mind, and the natural outflow of his thoughts, shaping his language spontaneously, and moulding it into characteristic forms of beauty and power.

When in 1842, on the eve of the Disruption, Chalmers met four or five hundred of his brethren in what was known as the Convocation, and endeavoured to reconcile them to the prospect of an unendowed church, the task was one that demanded the highest efforts of his eloquence. It was his aim to rouse them to an attitude worthy of the occasion, and, with that view, he concluded an appeal of transcendent power with a eulogy of enthusiasm which awakened thunders of applause. Never had he seemed more eloquent. Yet the passage that had so thrilled his audience was found after his death to be an exact transcript from one of his student discourses. 'Enthusiasm is a virtue rarely produced in a state of calm and unruffled repose. It flourishes in adversity. It kindles in the hour of danger and rises to deeds of renown. The terrors of persecution only serve to awaken the energy of its purposes. It swells in the pride of integrity, and great in the purity of its cause, it can scatter defiance amid a host of enemies.' – Already, 'fervet, immensusque ruit.'

In those days it was the practice of the members of the university to meet morning and evening in the public hall for worship, the prayers being led by the students of divinity. In his first theological session, Mr. Chalmers's prayer was an amplification of the Lord's Prayer, so eloquent and original as to awaken the wonder of all. One who remembered his prayers on these occasions said: 'The wonderful flow of eloquent, vivid, ardent description of the attributes and works of God, and still more, perhaps, the astonishingly harrowing delineation of the miseries, the horrid cruelties, immoralities, and abominations inseparable from war, which always came in more or less in connection with the bloody warfare in which we were engaged with France, called forth the wonderment of his hearers. He was then only sixteen years of age, yet he showed a taste and capacity for composition of the most glowing and eloquent kind. Even then his style was very much the same as at the period when he attracted so much notice, and made such powerful impression in the pulpit and by the press.'

Thus already, in his student days, that great outline of character had begun to shape itself, which, modified afterwards by new and powerful forces, made him the great man he was. The intensity of his nature, the redundant energy that hardly knew fatigue, the largeness of his view, the warmth of his affection, the independence of his judgment, and the gushing impetuosity of his style were manifest from these college days. Whatever he may have derived from his parents, or from the masters that taught him, or the books he read, a fearless, sturdy independence was the ruling feature – he was a genuine Scot.

On finishing his theological studies he accepted a situation as tutor in a family, under the feeling that, as his knowledge of mankind had hitherto been limited to his own family and his fellow-students, it was desirable for him to know a little more of the world. But his experience was not happy. It was not merely that his hours of teaching were so arranged as to leave him hardly any time for reading, but that his treatment was not what he considered due to a gentleman. Of such treatment he was sensitive to the last degree, nor was he restrained by any bashfulness or timidity from expressing his opinion of it. His employer wished to throw the blame on himself, and told him he had too much pride. He could not deny the charge, but showed a ready wit in hurling it back on his accuser. 'Sir,' was his undaunted reply, 'there are two kinds of pride: there is the pride which lords it over inferiors, and there is the pride which rejoices in repressing the insolence of superiors. The first I have none of – the second I glory in.' This, to say the least, was tolerably smart for a lad of eighteen. But it showed not only his independence but his intolerance of opposition. Soon after, he gave up the situation.

He had not completed his nineteenth year when he applied to his presbytery to be licensed as a probationer. He was under the legal age, but probably his precocity had made a considerable impression, for the law was evaded under a traditional exception in favour of youths 'of pregnant parts,' and on the 21st July 1799 he became a licentiate. But he did not show much interest in the work of his new calling. Immediately after, he paid a visit to friends in England, in the course of which he preached his first sermon, at Wigan, on 25th August 1799. His eldest brother wrote to his father: 'His mode of delivery is expressive, his language beautiful, and his arguments very forcible and strong… It is the opinion of those who pretend to be judges that he will shine in the pulpit, but as yet he is rather awkward in his appearance. We, however, are at some pains in adjusting his dress, manner, etc., but he does not seem to pay any great regard to it himself. His mathematical studies appear to occupy more of his time than his religious.'

Returning from England, he spent the next two winters at Edinburgh attending classes at the university. Mathematics, chemistry, natural and moral philosophy, and political economy were the subjects that occupied his attention. To Dr. Robison, Professor of Natural Philosophy, he felt himself under very deep obligations. He had been perplexed by the views which he found in the Système de la Nature, published under the pseudonym of Mirabeau, but really the work of the Baron von Holbach. That rigid uniformity of natural law which it enforced seemed to point ominously to materialism and atheism. Under Professor Robison's instructions he was led to ponder the remarkable harmony between the human mind and the processes of nature – the wonderful adaptation of the one to the other; and the conclusion was irresistible that this must be due to an intelligent Divine Being who had framed these adaptations. In after years this was the theme of his Bridgewater treatise, and it was one of the corner-stones of his Natural Theology. As to preaching during these Edinburgh studies, it seems to have been almost entirely neglected.

A new situation, however, opened up to him, as assistant to the Rev. Mr. Elliot, minister of Cavers, in Roxburghshire. The duties of this office he discharged for about a year with fair regularity and diligence, but without hard work, and without his showing any lively interest in the objects of the ministry. In the course of his residence there, he learned that when the parish of Kilmany, in Fife, should fall vacant (as it was likely to do, but not just immediately, by the appointment of the incumbent to a chair), he would get the presentation from the University of St. Andrews.

But what interested him much more was his appointment as assistant, for the ensuing session, to the professor of mathematics there. All that concerned the ministry excited but a languid interest, but his literary and scientific ambition was irrepressible. Already it had begun to look towards a mathematical chair. As Mrs. Oliphant remarks, 'The life and energy of a robust young man, full of ambition, eager for achievement, was in all his veins.' As a teacher he kindled the enthusiasm of his students for mathematical science. To himself the demonstrations of geometry were alike complete and beautiful. But he had also a way of associating mathematics with other pursuits, of bringing all manner of side-lights to bear on the study, of finding analogies in this quarter and in that, that greatly increased his popularity as a teacher. As one of his students remarked afterwards, 'Under his extraordinary management the study of mathematics was felt to be hardly less a play of the fancy than a labour of the intellect – the lessons of the day being continually interspersed with applications and illustrations of the most lively nature, so that he secured in a singular manner the confidence and attachment of his pupils.'

But such popularity among the students was apt to beget a different feeling among the professors; it especially roused Mr. Vilant, the gentleman as whose substitute Chalmers had been acting. Mr. Vilant, it appeared, had been granting certificates without communication with his assistant – a grievous offence in his eyes. Accordingly, at the public examination of his classes at the end of the session, Chalmers broke out into a severe invective against him, and delivered a long, sarcastic speech in condemnation of his conduct. The professors knew not how to look, but at last the Principal brought the speech of Chalmers to an end, and he proceeded with his examination as if nothing had happened.

His capacity of combining strong feeling in one direction with perfect self-control in every other was very remarkable. Many years afterwards, when expressing his views with extraordinary energy in the General Assembly on the question that led to the Disruption, he was interrupted by a layman, who remarked that they were all pleased to hear him, excited though he was, but that there were limits, etc., etc. 'Excited!' exclaimed Chalmers, in great astonishment; 'does the gentleman say that I am excited? I am as cool as an algebraic problem.' His head was in no degree disturbed by the vehemence of his heart.

A short time had to elapse between the close of the session and his ordination as minister of Kilmany, which Mr. Chalmers devoted to a visit to Edinburgh. His father was disappointed and mortified that on the eve of entering on so solemn a profession, he did not put the interval to use at home in the way of earnest meditation and prayer. For that, however, the son did not see the slightest necessity. He deemed himself already sufficiently prepared for his duties, with the nature of which he was well acquainted. In this strain he wrote to his father, adhering to his plan. A few years later he would have felt most differently, and, ashamed of his carelessness, he would have most cordially fallen in with all that his father had written.