A mistaken assumption many people make is believing that the early church fathers were Roman Catholics in their understanding of salvation and it wasn’t until Martin Luther that justification by faith alone was taught. This is an oversimplification that does not take into consideration that the church fathers disagreed among themselves on many issues and were often inconsistent in their beliefs. Certain beliefs such as papal infallibility and the bodily assumption of Mary were completely unknown in the first four centuries of the church. One of the theological controversies of the early church and middle ages was attempting to reconcile justification by faith and yet still retain a regenerative understanding of baptism. Luther himself was inconsistent in affirming justification by faith alone while still believing in baptismal regeneration for infants. The following quotes demonstrate that justification by faith was a central belief among the church fathers:
“They all therefore were glorified and magnified, not through themselves or their own works or the righteous doing which they wrought, but through His will. And so we, having been called through His will in Christ Jesus, are not justified through ourselves or through our own wisdom or understanding or piety or works which we wrought in holiness of heart, but through faith, whereby the Almighty God justified all men that have been from the beginning; to whom be the glory forever and ever” (Chapter 32).
“For His Cross, for His death, and His resurrection, and the faith which is through Him, are my unpolluted monuments, and in these . . . I am willing to have been justified” (Philadelphians, Chapter 8).
“I know that through grace you are saved, not of works, but by the will of God, through Jesus Christ” (Philippians).
The Epistle to Diognetus
“For what, save His righteousness, could cover our sins? In whom could we be justified, save in the Son of God alone?” (Chapter 9).
“Not by these works, but by faith, a man is justified as was Abraham . . . in no other manner can there be redemption” (As cited in James Buchanan, The Doctrine of Justification, 94).
Basil of Caesarea
“This is perfect and pure boasting in God, when one is not proud on account of his own righteousness but knows that he is indeed unworthy of the true righteousness and is justified solely by faith in Christ” (Homilia XX, Homilia De Humilitate).
“When an ungodly man is converted, God justifies him through faith alone, not on account of good works, which he possessed not; otherwise, on account of his ungodly deeds, he ought to have been punished” (Commentary on Romans 10:3; PL 30:692D).
“But what is the ‘law of faith?’ It is, being saved by grace. Here he shows God’s power, in that He has not only saved, but has even justified, and led them to boasting, and this too without needing works, but looking for faith only” (Homily on Romans 3:19).
“How then can the Jews think that they have been justified by the works of the law in the same way as Abraham, when they see that Abraham was not justified by the works of the law but by faith alone? Therefore there is no need of the law when the ungodly is justified before God by faith alone” (Commentary on Paul’s Epistles, CSEL 81:131).
“God has decreed that a person who believes in Christ can be saved without works. By faith alone he receives the forgiveness of sins” (Commentary on 1 Corinthians 1:4).
Cyril of Alexandria
“For we are justified by faith, not by works of the law, as Scripture says (Gal 2:16). By faith in whom, then, are we justified? Is it not in him who suffered death according to the flesh for our sake? Is it not in one Lord Jesus Christ?” (Against Nestorius).
“If God would justify you, say, ‘Lord, I plead the death of our Lord Jesus Christ between me and thy judgment’ . . . cover thyself with this alone” (As cited in John Owen, The Doctrine of Justification by Faith, 4).
For more examples, see this article.