Recently a reader asked whether or not Constantine should be recognized as a Christian since there is evidence he mixed paganism with Christianity and implemented anti-Semitic policies towards the Jewish peoples. Below was my response that might serve useful for you as well.
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Caesar Flavius Valerius Aurelius Constantinus Augustus (27 February c. 272 – 22 May 337), is known to many in English as Constantine I, Constantine the Great, or Saint Constantine. He served as the Roman Emperor from 306, but did not gain sole rulership until 324 where he ruled singularly until his death in 337. Constantine is best known for being the first Christian Roman emperor.
The Byzantine liturgical calendar, observed by the Eastern Orthodox Church and Eastern Catholic Churches of Byzantine rite, lists both Constantine and his mother Helena as saints. Although he is not included in the Latin Church’s list, he is honored with the title "The Great" for his many contributions to the advancement of the Christian religion.
The evidence supporting some change in nature in his view of Jesus Christ and the church is reflected in his actions as ruler. That is to say, he reversed the trend of persecuting Christians for which his predecessor, Diocletian, is well known. Furthermore, he issued the Edict of Milan in 313, with co-emperor Licinius, which proclaimed religious toleration throughout the empire and was baptized a Christian on his deathbed.
Some critics of Constantine doubt he was truly converted to Christ and insist that he be condemned and damned. Evidence to support this claim is rooted in the fact that Constantine merged paganism with Christianity and that he was an anti-Semite.
In a short history of the church, it is impossible to detail all the arguments for the possible genuine conversion of Constantine and his importance in the history and life of the church, or to explore all the objections to counting him among the saints.
Mixing pagan traditions with Christianity, excessive cruelty, and anti-Semitism are charges that have been leveled not only against Constantine, but the church as a whole many times over by her critics due to official church policies and practices over the centuries, reflected in part by the Inquisition and Crusades. The Protestants are not excluded from the same general accusations. The Anabaptist were drowned, others were tortured for not holding certain religious beliefs regarding freedom of worship, and Jews were often looked down upon.
For example, in 1543 Luther published On the Jews and Their Lies in which he says that the Jews are a "base, whoring people, that is, no people of God, and their boast of lineage, circumcision, and law must be accounted as filth." Again, "They are full of the "devil's feces ... which they wallow in like swine." The synagogue was a "defiled bride, yes, an incorrigible whore and an evil slut ..." Luther argues why it is proper that their synagogues and schools be set on fire, their prayer books destroyed, rabbis forbidden to preach, homes razed, and property and money confiscated. They should be shown no mercy or kindness, afforded no legal protection, and these "poisonous envenomed worms" should be drafted into forced labor or expelled for all time. He also seems to advocate their murder, writing "[w]e are at fault in not slaying them."
Initially, Luther seemed to be sympathetic to the Jews, especially in their resistance to the Roman Catholic Church. He wrote, early in his career:
"The Jews are blood-relations of our Lord; if it were proper to boast of flesh and blood, the Jews belong more to Christ than we. I beg, therefore, my dear Papist, if you become tired of abusing me as a heretic, that you begin to revile me as a Jew."
However, when the Jews refused to convert to Christianity and embrace the Protestant movement, he turned violently against them. Luther’s writing against what should be done to the peasants is equally disturbing. In a tract, Against the Murderous, Thieving Hordes of Peasants (1525), Luther encouraged the nobility to visit swift and bloody punishment upon the peasants. The German princes were advised to "crush, stab, smite, slay all you can; you will win heaven more easily by bloodshed than prayer."
We can move on throughout history and question the true conversion of other important figures such as George Washington and Abraham Lincoln. There is controversy surrounding whether or not Washington took communion, or gave a public testimony of his personal faith in Christ as Lord and Savior. From The Writings of Thomas Jefferson, vol. 1, p. 284 comes this interesting document.
"Feb. 1. Dr. Rush tells me that he had it from Asa Green that when the clergy addressed General Washington on his departure from the Government, it was observed in their consultation that he had never on any occasion said a word to the public which showed a belief in the Christian religion and they thought they should so pen their address as to force him at length to declare publicly whether he was a Christian or not. They did so. However, he observed, the old fox was too cunning for them. He answered every article in their address particularly except that, which he passed over without notice…. " I know that Gouverneur Morris, who pretended to be in his secrets and believed himself to be so, has often told me that General Washington believed no more in the system (Christianity) than he did"
Lincoln’s law partner and biographer was William Herndon (December 25, 1818, Kentucky - March 18, 1891, Springfield, Illinois). Following the president’s death, Mr. Herndon gave public lectures on Mr. Lincoln’s skepticism of the Christian faith. The following letter appeared, in 1870, in the Index, a journal published in Toledo, Ohio, and edited by Francis E. Abbott: "Mr. Abbott: Some time since I promised you that I would send you a letter in relation to Mr. Lincoln's religion. I do so now. Before entering on that question, one or two preliminary remarks will help us to understand why he disagreed with the Christian world in its principles as well as in its theology". Herndon follows with a lengthy discussion of Mr. Lincoln’s beliefs.
And what shall we say of John Calvin and his rule in Geneva resulting in the death of many citizens at the hands of the state—over which he had great influence? The death of Servetus in 1553 is but one famous example. Servetus had been warned not to come to Geneva. In a letter to a friend, Calvin warned: Servetus lately wrote to me and coupled with his letter a long volume of his delirious fancies...He would like to come here if it is agreeable to me. But I do not wish to pledge my word for his safety. For, if he comes, I will never let him depart alive, if I have any authority..."
I do not mean to cast aspersions upon Luther, Calvin, Washington, or Lincoln. What I do mean is that only God knows the heart. The good a person does can often be countered by the evil [injury] they do to self and others, and cause others to question their sincerity.
Regarding Constantine in particular, however, I know the question of his conversion is controversial and is open to concern, and so at the time of writing I tried to be fair and balanced in the text.
"Constantine believed he had won the battle because he had received help from the God of the Christians. He too would become a Christian and worship the true Light of the world. Whether or not Constantine was indeed converted has been a subject of great debate. Certainly he was very tolerant toward Christians." Etc.
I would leave the matter at that without drawing any ultimate conclusions for if the narrative of the church teaches anything it reminds us that, "the best of men are at best men."
It is easy to sit in the comfort and security of a twenty-first century, Western cultural perspective and pass judgment upon people and events that took place long ago, without understanding the society in which they lived, or the dynamics that shaped their personalities. My own counsel is to be more cautious, and as gracious as possible, in judging the ultimate destiny of individuals.
We are all in the hands of God.
I hope these thoughts help.