The awful mysteries of the Christian faith and worship were concealed from the eyes of strangers, and even of catechu mens, with an affected secrecy, which served to excite their wonder and curiosity. But the severe rules of discipline which the prudence of the bishops had instituted, were relaxed by the same prudence in favor of an Imperial proselyte, whom it was so important to allure, by every gentle condescension, into the pale of the church; and Constantine was permitted, at least by a tacit dispensation, to enjoy most of the privileges, before he had contracted any of the obligations, of a Christian. Instead of retiring from the congregation, when the voice of the deacon dismissed the profane multitude, he prayed with the faithful, disputed with the bishops, preached on the most sublime and intricate subjects of theology, celebrated with sacred rites the vigil of Easter, and publicly declared himself, not only a partaker, but, in some measure, a priest and hierophant of the Christian mysteries. The pride of Constantine might assume, and his services had deserved, some extraordinary distinction: and ill-timed rigor might have blasted the unripened fruits of his conversion; and if the doors of the church had been strictly closed against a prince who had deserted the altars of the gods, the master of the empire would have been left destitute of any form of religious worship. In his last visit to Rome, he piously disclaimed and insulted the superstition of his ancestors, by refusing to lead the military procession of the equestrian order, and to offer the public vows to the Jupiter of the Capitoline Hill. Many years before his baptism and death, Constantine had proclaimed to the world, that neither his person nor his image should ever more be seen within the walls of an idolatrous temple; while he distributed through the provinces a variety of medals and pictures, which represented the emperor in an humble and suppliant posture of Christian devotion.
The pride of Constantine, who refused the privileges of a catechumen, cannot easily be explained or excused; but the delay of his baptism may be justified by the maxims and the practice of ecclesiastical antiquity. The sacrament of baptism was regularly administered by the bishop himself, with his assistant clergy, in the cathedral church of the diocese, during the fifty days between the solemn festivals of Easter and Pentecost; and this holy term admitted a numerous band of infants and adult persons into the bosom of the church. The discretion of parents often suspended the baptism of their children till they could understand the obligations which they contracted: the severity of ancient bishops exacted from the new converts a novitiate of two or three years; and the catechumens themselves, from different motives of a temporal or a spiritual nature, were seldom impatient to assume the character of perfect and initiated Christians. The sacrament of baptism was supposed to contain a full and absolute expiation of sin; and the soul was instantly restored to its original purity, and entitled to the promise of eternal salvation. Among the proselytes of Christianity, there are many who judged it imprudent to precipitate a salutary rite, which could not be repeated; to throw away an inestimable privilege, which could never be recovered. By the delay of their baptism, they could venture freely to indulge their passions in the enjoyments of this world, while they still retained in their own hands the means of a sure and easy absolution. The sublime theory of the gospel had made a much fainter impression on the heart than on the understanding of Constantine himself. He pursued the great object of his ambition through the dark and bloody paths of war and policy; and, after the victory, he abandoned himself, without moderation, to the abuse of his fortune. Instead of asserting his just superiority above the imperfect heroism and profane philosophy of Trajan and the Antonines, the mature age of Constantine forfeited the reputation which he had acquired in his youth. As he gradually advanced in the knowledge of truth, he proportionally declined in the practice of virtue; and the same year of his reign in which he convened the council of Nice, was polluted by the execution, or rather murder, of his eldest son. This date is alone sufficient to refute the ignorant and malicious suggestions of Zosimus, who affirms, that, after the death of Crispus, the remorse of his father accepted from the ministers of christianity the expiation which he had vainly solicited from the Pagan pontiffs. At the time of the death of Crispus, the emperor could no longer hesitate in the choice of a religion; he could no longer be ignorant that the church was possessed of an infallible remedy, though he chose to defer the application of it till the approach of death had removed the temptation and danger of a relapse. The bishops whom he summoned, in his last illness, to the palace of Nicomedia, were edified by the fervor with which he requested and received the sacrament of baptism, by the solemn protestation that the remainder of his life should be worthy of a disciple of Christ, and by his humble refusal to wear the Imperial purple after he had been clothed in the white garment of a Neophyte. The example and reputation of Constantine seemed to countenance the delay of baptism. Future tyrants were encouraged to believe, that the innocent blood which they might shed in a long reign would instantly be washed away in the waters of regeneration; and the abuse of religion dangerously undermined the foundations of moral virtue.
The gratitude of the church has exalted the virtues and excused the failings of a generous patron, who seated Christianity on the throne of the Roman world; and the Greeks, who celebrate the festival of the Imperial saint, seldom mention the name of Constantine without adding the title of equal to the Apostles. Such a comparison, if it allude to the character of those divine missionaries, must be imputed to the extravagance of impious flattery. But if the parallel be confined to the extent and number of their evangelic victories the success of Constantine might perhaps equal that of the Apostles themselves. By the edicts of toleration, he removed the temporal disadvantages which had hitherto retarded the progress of Christianity; and its active and numerous ministers received a free permission, a liberal encouragement, to recommend the salutary truths of revelation by every argument which could affect the reason or piety of mankind. The exact balance of the two religions continued but a moment; and the piercing eye of ambition and avarice soon discovered, that the profession of Christianity might contribute to the interest of the present, as well as of a future life. The hopes of wealth and honors, the example of an emperor, his exhortations, his irresistible smiles, diffused conviction among the venal and obsequious crowds which usually fill the apartments of a palace. The cities which signalized a forward zeal by the voluntary destruction of their temples, were distinguished by municipal privileges, and rewarded with popular donatives; and the new capital of the East gloried in the singular advantage that Constantinople was never profaned by the worship of idols. As the lower ranks of society are governed by imitation, the conversion of those who possessed any eminence of birth, of power, or of riches, was soon followed by dependent multitudes. The salvation of the common people was purchased at an easy rate, if it be true that, in one year, twelve thousand men were baptized at Rome, besides a proportionable number of women and children, and that a white garment, with twenty pieces of gold, had been promised by the emperor to every convert. The powerful influence of Constantine was not circumscribed by the narrow limits of his life, or of his dominions. The education which he bestowed on his sons and nephews secured to the empire a race of princes, whose faith was still more lively and sincere, as they imbibed, in their earliest infancy, the spirit, or at least the doctrine, of Christianity…..(The History of the decline and Fall of the Roman Empire, Vol. 2, Chap. 20, pgs. 270 - 275 of the Everyman’s Library edition)