“Those who do not obey Him, but being disinherited by Him, have ceased to be His sons.” [Against Heresies 4.41.3]
“We should fear ourselves, least perchance after [we have come to] the knowledge of Christ, if we do things displeasing to God, we obtain no further forgiveness of sins, but are shut out from His Kingdom. And for that reason, Paul said, ‘For if [God] spared not the natural branches, [take heed] lest He also not spare you” (Romans 11:21). [Against Heresies 4.27.2]
“It is not to those who are on the outside that he said these things, but to us – LEST WE SHOULD BE CAST FORTH FROM THE KINGDOM OF GOD, by doing any such thing.” [Against Heresies 4.27.4]
“Knowing that WHAT PRESERVES HIS LIFE, NAMELY, OBEDIENCE TO GOD, is good, he may diligently keep it with all earnestness.” [Against Heresies 4.39.1]
“The world returned to sin…and so it is destined to fire. So is the man who after baptism renews his sins.” [On Baptism, Ch. 8]
“We ought indeed to walk so holily, and with so entire substantially of faith, as to be confident and secure in regard of our own conscience, desiring that it may abide in us to the end. Yet, we should not presume [that it will]. For he who presumes, feels less apprehension. He who feels less apprehension, takes less precaution. He who takes less precaution, runs more risk. Fear is the foundation of salvation. Presumption is the impediment to fear…More useful, then, is it to apprehend that WE MAY POSSIBLY FAIL, than to presume that we cannot. For apprehending will lead us to fear, fear to caution, and caution to salvation. On the other hand, if we presume, there will be neither fear nor caution to save us.” [On the Apparel of Women, Book 2, Chapter 2]
“He saw that MOST PERSONS – AFTER OBTAINING SALVATION – WOULD BE LOST AGAIN, by soiling the wedding dress, by failing to provide oil for their torches.” [Scorpiace, Ch. 6]
COMMODIANUS (A. D. 240)
“Being a believing man, if you seek to live as the Gentiles do, the joys of the world remove you from the grace of Christ.” [On Christian Discipline, LVII: “That Worldly Things are Absolutely to Be Avoided.”]
ORIGEN (d. 253) – I know Origen was a heretic, but his comment is valuable for its historical value; and how it exposes that “eternal security” or the “once saved, always saved” teaching, really comes from the Gnostics…
“Certain ones of those [Gnostics] who hold different opinions misuse these passages. They essentially destroy free will by introducing ruined natures incapable of salvation and by introducing others as being saved in such a way that they cannot be lost.” [De Principiis, Book 3, Ch. 1.8]
“Only let not Christ be forsaken, so that THE LOSS OF SALVATION and of an eternal home would be feared.” [Treatise 3, Ch. 10]
“Faith itself and the saving birth do not make alive by merely being received. Rather, they must be preserved…The Lord taught this in His instruction when He said…“Sin no more, lest a worst thing come upon you” (John 5:14)…SOLOMON, SAUL, and many others were able to keep the grace given to them so long as they walked in the Lord’s ways. However, when the discipline of the Lord was forsaken by them, grace also forsook them.” [Epistle 6.2]
“Whoever that confessor is, he is not greater, better, or dearer to God than SOLOMON. Solomon retained the grace that he had received from the Lord, as long as he walked in God’s ways. However, AFTER HE FORSOOK THE LORD’S WAY, HE ALSO LOST THE LORD’S GRACE. For that reason it is written, ‘Hold fast that which you have, lest another take your crown’ (Revelation 3:11)…’He that endures to the end, the same shall be saved’ (Matthew 10:22).” [Treatise 1.20-21]
“Even a baptized person LOSES THE GRACE that he has attained, unless he remains innocent.” [Treatise 12.3.27]
APOSTOLIC CONSTITUTIONS (A. D. 390)
“He who sins after his baptism, unless he repent and forsake his sins, shall be condemned to Hell-fire.” [Book 2.3.VII: “What Ought to Be the Character of the Initiated.”]
AUGUSTINE & JOHN CALVIN:
ORIGINATORS OF “ONCE SAVED, ALWAYS SAVED”
Martin Luther and John Calvin (d. 1564), the two great theological leaders of the Protestant Reformation, were both heavily influenced by the theology of Augustine (d. 430). Augustine lived at the end of this line of early fathers. He denied their doctrine on apostasy, and instead affirmed in his book The Gift of Perseverance the “once saved, always saved” teaching. Critics of Augustine, have since declared that the fact he was an ex-Gnostic, proves that his “once saved, always saved” belief came from Gnosticism. And, if we take the above quote from Origen seriously, that seems to be the case. All of the Puritans take their theology from Calvin:–and all Reformed Christians, Baptists, and Presbyterians with the Westminster Confession of Faith, etc., take their theology from Calvin, hence “once saved, always saved,” the Gnostic belief, was mediated to modern Calvinists through Augustine, Calvin, and the Puritans!
MARTIN LUTHER & JOHN WESLEY:
REAFFIRM THAT CHRISTIANS CAN LOSE THEIR SALVATION
“We must continuously seek after Him; indeed, we must seek Him evermore, as the Psalmist says in Psalm 105:4: “Seek the Lord…seek His face evermore.” Those who do not make progress in seeking after God, are bound to RETROGRESS; indeed, those who do not seek, will LOSE that which they already have obtained. We must never stand still in seeking after God.”
“Others who in the beginning lead a pious life and do many good works are not saved (Saul: 1 Samuel 13:13)…compare for this also Judas (Matthew 26:14).”
“Here are rejected those who teach that those who have once been holy cannot fall again.” [Augsburg Confession, Article XII: “Of Repentance”]
John Wesley (d. 1791), agreeing with Luther, was more emphatic about warning that a saved Christian can lose his salvation. Thomas Oden, the Wesleyan scholar, summarizes the Biblical basis for the possibility of losing salvation (apostasy), from John Wesley’s Predestination Calmly Considered:
“Those who, having once truly believed and been endued with the faith that produces a good conscience, may later fall (Ezek. 18:24; 1 Tim. 1:18, 19). Those once grafted into the good olive tree may later be broken off through willful unbelief (Rom. 11:16-22). Branches that ‘abide not’ are cast forth and burned (John 15:6). Those having once known Christ can again become entangled in the world (2 Peter 2:20). Those who have been made partakers of the Holy Spirit and have produced fruits of the Spirit may nevertheless fall from grace back into former pollutions (Heb. 6:4-6; 10:29). Even those most actively receiving sanctifying grace may yet fall (Heb. 10:26-29). We share finally in Christ only if we hold to our first confidence (Heb. 3:14). We are instructed to take care that we do not lose what we have (2 John 8), to hold fast so that no one seizes the crown (Rev. 3:11). Grace is almighty but not irresistible.”
 Martin Luther, “Commentary on Romans 3:11” in Commentary on Romans. Translated by J. Theodore Mueller (Grand Rapids, MI: Kregel Publications, 1976), p. 71.
 Ibid., “Commentary on Romans 8:28,” p. 130.
 Thomas Oden, John Wesley’s Scriptural Christianity (Grand Rapids, MI: Zondervan, 1994), pp. 269-270. Wesley follows the teaching of the Church of England (Thomas Cranmer, The Thirty-Nine Articles XVI: “Of Sin after Baptism”), which also agrees with the Lutheran Church (Martin Luther, Augsburg Confession XII: “Of Repentance”). But Wesley differs from Calvinists or Puritans (Westminster Confession of Faith XVII, “Of the Perseverance of the Saints”).
For more evidence of conditional security among the church fathers, see Thomas Oden’s The Transforming Power of Grace, ch. 8: “Election Made Sure Through Faith.”