Both “better angel” and “better angels” have long pedigrees in English literature, though there is some disagreement as to whether an individual person has only one better angel or many, and conversely whether many people collectively have multiple better angels or just one.
My better angel
The phrase “my better angel” has been in use since the very late sixteenth century. From William Shakespeare, “The Passionate Pilgrime” (aka Sonnet 144) (1599):
Two Loves I have, of Comfort and Despaire,/ That like two Spirits do suggest me still:/ My better Angell is a Man (right faire)/ My worser spirite a woman (colour’d ill.)/ To winne me soone to hell, my female evil/ Tempteth my better Angel from my side,/ And woulde corrupt my Saint to be a Devil,/ Wooing his purity with her faire Pride.
From Nathanael Lee, The Massacre of Paris (1734):
King. Let then the World be witness,/ All that is Honest, Sacred, Good and Just,/ Be Witnesses the Powers of Heav’n and earth,/ With this Embrace I pardon thee thy Errors,/ I bid thee welcome, as my better Angel:/ Thou shalt direct in all my Bosom Councils;/ My Genius ; O! and while I hold thee thus,/ Methinks I press my Father in my Arms.
From William Guthrie, The Friends: A Sentimental History (1754) [combined snippets]:
Daughters, said he, thou hast acted like my better Angel : Henceforth I resign myself to your Conduct : If you are sure of your Friend, you may trust her with the mighty Secret : Perhaps it may be necessary : In the mean while, recompose yourself, and whatever Concern you take in my Fate, will be justified by the Service I was so happy to do to you and your Friend.
From Henry Jones, The Earl of Essex (1753):
ESSEX. O Sounds angelic! Goodness undeserv’d!/ My swelling Heart can keep no Bounds, my Soul/ Flows o’er.—And will my gracious Queen forgive me?/ Oh let me prostrate thus before you fall,/ My better Angel, and my Guardian Genius!/ Permit me, royal Mistress, to renounce/ My faithful Sentiments, my Soul's true Dictates;/ Vouchsafe your Essex but this one Request,/ This only Boon, he’ll thank you with his last,/ His dying Breath, and bless you in his Passage.
ESSEX. Such cold philosophy the heart disdains;/ And friendship shudders at the moral tale./ My friend, the fearful precipice is past,/ And danger dare not meet us more. Fly swift/ Ye better Angels, waft the welcome tidings/ Of pardon, to my friend; of life and joy.
My better angels
The phrase “my better angels” does occur in the years before Lincoln’s speech, but it is far less common. From “Epilogue [to Dr. Stratford’s play, Lord Russel],” in The London Magazine (September 1784), in which the "better angels" appear to be the audience at the play:
Away then, fear, despondency, and doubt,/ My better angels drive such traitors out;/ Command our labours, and let your desire/ Forbid that Russel should again expire.
And from Benjamin Webster, The Golden Farmer; or, The Last Crime (by 1832), in which the "better angels" are the farmer's wife and daughter:
Farmer. Bless ye——bless ye both. (Kissing them.) You've proved my better angels. Ere I knew yon, ay, and since, for a time, the vice of gain, either by honest or dishonest means, had taken possession of my breast to an almost miserly feeling ; but your bright example has taught my heart to flow with better thoughts.
But overall, “my better angel” is far more common than “my better angels.”
His better angel
Anne Marsh-Caldwell explains what may have been a widespread understanding of the term “better angel” in Mordaunt Hall (1849):
His better angel — all men have their better angel ; long lingers the celestial visitant before it finally takes flight — his better angel urged him to come back, to catch that forlorn and betrayed one, that generous, affectionate, loving heart to his, and to ratify before God and society those hallowed bonds which united them to each other.
But the evil counselor within triumphed : the tempter whispered of ridicule, obstruction, embarrassment...
Good wins out in the following excerpt from The Ladies Cabinet of Fashion, Music & Romance (1832):
As he [Wernerstoff] at once formed his decision to obey his better angel, his spirit, previously clogged by the dull, heavy weights of combined misery and despair, seemed now of ethereal lightness and buoyancy. His tempter saw and trembled in impotent malice.
Fifteen years later, “The Maid, Wife and Mother,” in the same periodical (March 1847) presents woman as the personification of man’s better angel:
But it is needless to multiply examples. Every day’s experience and observation may convince us of the influence of woman, in the relations of mother, wife, sister, daughter, friend—in fortune, fame, fashion, religion and happiness. She was given to man, as his better angel, to dissuade him from vice, to stimulate him to virtue, to make home delightful, and life joyous; and when in the exercise of these gentle and holy charities, she fulfils her high vocation.
Better angels of the human heart
Edward Bulwer-Lytton, “Cromwell’s Dream,” (by 1839) asserts the presence of multiple better angels in the human heart:
“Behold,” the Demon cried, “the Future Cromwell, there!/ Art thou content, on Earth, the Greatest thou,/ APOSTATE AND USURPER?”—From his rest/ The Dreamer started with a heaving breast,/ The better angels of the human heart/ Not dumb to his,—The Hell-Born laugh’d aloud/ And o’er the Evil Vision rush’d the Cloud!
Our better angels
In a Google Books search, the collectively understood “our better angels” appears as early as 1633. From Henry Viscount Faulkland, “The Life of Edward the Second” (by 1633) in The Harleian Miscellany (1744):
The sad Impressions of these Disorders, and the reeking Blood of so many noble and brave Subjects, so basely spilt, do seem to cry for Vengeance. This, for a While, wrought deeply in his distressed Thoughts, but a small Intermission brings him back to his former Temper. A customary Habit of a depraved Nature dulleth the Sense of the Soul and Conscience; so that, when our better Angels summon us to Repentance, the Want of a lively true Apprehension leads us blindfold into a dangerous despairing Hazard.
From William D'avenant, The Unfortunate Lovers (licensed April 1638, printed 1643):
Altophil. I am the cause of all thy grief ; make haste,/ 'Tis fit I dye———
Amaranta. That sentence is my doom——— [She falls on the sword]
Altophil. Hold, Amaranta, hold!/ Where are our better Angels at such times/ As these? sweet Virgin, breathe awhile!——
Amaranta. Go tell Arthiope she needs not fear/ Her Rival now, my Bridal Bed is in the Earth.
From John Fryer, “A Relation of the Canatick-Country” (by 1676) in A New Account of East-India and Persia, in Eight Letters (1698):
But having conquered by our better Angels this lively portraiture of Hell, we were led into an happy Elysium, or Plain, that was bounded by the immense Ocean ; and had we been Shades, to have been satisfied with an Aierial Diet, we might have fared well, for nothing else could we purchase, the poor Inhabitants being Fishermen, were left by the iniquity of [General] Delvi, without either Fish, Boats, Nets, or Rice ; and upon that account unlikely to supply us.
From Nicholas Rowe, The Tragedy of the Lady Jane Gray (1715):
Earl of Pembroke. Then sure our better Angels called me hither./ For this is Friendship’s Hour, and Friendship’s Office,/ To come when Counsel and when Help is wanting,/ To share the Pain of every gnawing Care,/ To speak of Comfort in the Time of Trouble,/ To reach a Hand, and save thee from Adversity.
From “Song, By a Gentleman in London. Addressed to his Wife in the Country,” in The Scots Magazine (April 1761):
Let the wanton wits deride it,/ HUSBAND is a charming name:/ None can say, but who has try’d it,/ How enjoyment feeds the flame./ WIVES our better angels are,/ Angels in their loveliest dress,/ Gentle soothers of our care,/ Smiling guardians of our peace.
Our better angel
As for the notion of a collective “better angel” for a multitude of people, an early example appears in Thomas Killigrew, Bellamira her Dream: or, The Love of Shadows, Part 2 (1663):
Pollidor. 'Tis the fame ; look Phillora, here's our better Angel [a painted portrait] come again ; so, now I defie Fortune and all her falshood ; frown on, here's my peace which I'll not give for all thy smiles; how I love my eyes now, better then I did my hands before! they faithfully held their hold, while these like cowards let thee go ; ‘tis the noblest sense of any, and informs the knowing soul, makes acquaintance betwixt us and the great works of heaven, and obliges our hearts more then all the rest ;
And a later example appears in William Whewell, On the Foundations of Morals: Four Sermons Preached before the University of Cambridge, November, 1837 (1839):
We speak of man’s natural desires worse than thy deserve, and yet will not have any other master. We not only refuse to listen to our better angel, but drive him from us with mocks and insults. We plunge willingly into the slough of selfishness, and refuse to pass onwards ; trusting to some vain alchemy which may convert it into a cleansing fountain.
But again, the more common trope involves “our better angels,” as a counterpart to the preferred “my better angel.”
Better angels in the years leading up to March 3, 1861
Two later occurrences of “our better angels” may have influenced Lincoln’s use of “our better angels” in his 1861 inaugural address. From Charles Dickens, Barnaby Rudge (1841):
It is curious to imagine these people of the world, busy in thought, turning their eyes toward the countless spheres that shine above us. The man who lives but in the breath of princes, has nothing in his sight but stars for courtiers’ breasts. The envious man beholds his neighbours’ honours in the sky ; to the money-hoarder, and the mass of worldly folk, the whole great universe above glitters with sterling coin — fresh from the mint — stamped with the sovereign's head — coming always between them and Heaven, turn where they may. So do the shadows of our own desires stand between us and our better angels, and thus their brightness is eclipsed.
From Frederic Huntington, “National Retribution, and the National Sin” (“Preached on Fast Day, 1851, soon after the passage, in Congress, of the bill known as the ‘Fugitive Slave Law’”), in Sermons for the People (Boston: 1857):
Herein is another working of the everlasting law. With every wanton denial of our purer aspirations, those aspirations themselves grow faint. Resistance to our better angels drives those angels away. If we cast insults on our power of moral discrimination, the power itself will perish. No nation can smother, whether in the legislative council, the fashions of society, the iniquities of trade, or the oppressive enactments of the statute-book, those eternal sentiments which rise up to bear their melancholy witness, even in debauched and degraded souls, without realizing in the very act a punishment infinitely more dismal than any defeat of its armies or any damage to the credit of its treasury.
By the time of Lincoln’s inaugural address of 1861, “our better angels” was a figure of speech familiar to many citizens of the United States. The phrase would have called forth the notions of enlightened, calm, and virtuous judgment—the best guides to sensible and honorable conduct in any person or nation.