By John Newton:
Wherever and whenever the doctrines of free grace and justification by faith have prevailed in the Christian church, and according to the degree of clearness with which they have been enforced, the practical duties of Christianity have flourished in the same proportion. Wherever they have declined, or been tempered with the reasonings and expedients of men, either from a well-meant (though mistaken) fear lest they should be abused, or from a desire to accommodate the Gospel, and render it more palatable to the depraved taste of the world, the consequence has always been an equal declension in practice.
So long as the Gospel of Christ is maintained without adulteration, it is found sufficient for every valuable purpose; but when the wisdom of man is permitted to add to the perfect work of God, a wide door is opened for innumerable mischiefs—the divine commands are made void, new inventions are continually taking place, zeal is diverted into a wrong channel, and the greatest stress laid upon things, either unnecessary or unwarrantable. Hence, perpetual occasion is given for strife, debates, and divisions, till at length the spirit of Christianity is forgot, and the power of godliness lost, amidst fierce contentions for the form.
To sum up this inquiry in few words. The Gospel is a wise and gracious dispensation, equally suited to the necessities of man and to the perfections of God. It proclaims relief to the miserable, and excludes none but those who exclude themselves. It convinces a sinner that he is unworthy of the smallest mercy, at the same time that it gives him a confidence to expect the greatest. It cuts off all pretence of glorying in the flesh, but it enables a guilty sinner to glory in God. To them that have no might, it increases strength; it gives eyes to the blind, and feet to the lame; subdues the enmity of the heart, shows the nature of sin, the spirituality and sanction of the law with the fullest evidence; and, by exhibiting Jesus as made of God, wisdom, righteousness, sanctification, and redemption to all who believe, it makes obedience practicable, easy, and delightful.
The constraining love of Christ engages the heart and every faculty in his service. His example illustrates and recommends his precepts, his presence inspires courage and activity under every pressure, and the prospect of the glory to be revealed is a continual source of joy and peace, which passeth the understanding of the natural man. Thus the Gospel filleth the hungry with good things, but it sendeth the rich and self-sufficient empty away, and leaves the impenitent and unbelieving in a state of aggravated guilt and condemnation.
From John Newton, The Works of Rev. John Newton, 4 vols. (New Haven: Whiting, 1824), 2:270.