Barnabas - A.D. 70 -
He who keeps them will be glorified in the kingdom of God. However, he who chooses other things will be destroyed with his works. -Only those who fear the Lord and keep His commandments have life with God; but as for those who do not keep His commandments, there is no life in them. -We ought therefore, brethren, carefully to inquire concerning our salvation. Otherwise, the wicked one, having made his entrance by deceit, may hurl us forth from our life.
Justin Martyr- 100 -168 AD - was martyred by beheading. His works are earliest sizeable Christian apologetics:
Man acts by his own free will and not by fate. (20) We have learned from the prophets, and we hold it to be true, that punishments, chastisements, and rewards are rendered according to the merit of each man’s actions. Otherwise, if all things happen by fate, then nothing is in our own power. For if it be predestined that one man be good and another man evil, then the first is not deserving of praise or the other to be blamed. Unless humans have the power of avoiding evil and choosing good by free choice, they are not accountable for their actions-whatever they may be…. For neither would a man be worthy of reward or praise if he did not of himself choose the good, but was merely created for that end. Likewise, if a man were evil, he would not deserve punishment, since he was not evil of himself, being unable to do anything else than what he was made for. (21)
But that you may not have a pretext for saying that Christ must have been crucified, and that those who transgressed must have been among your nation, and that the matter could not have been otherwise, I said briefly by anticipation, that God, wishing men and angels to follow His will, resolved to create them free to do righteousness; possessing reason, that they may know by whom they are created, and through whom they, not existing formerly, do now exist; and with a law that they should be judged by Him, if they do anything contrary to right reason: and of ourselves we, men and angels, shall be convicted of having acted sinfully, unlesswe repent beforehand. But if the word of God foretells that some angels and men shall be certainly punished, it did so because it foreknew that they would be unchangeably [wicked], but not because God had created them so.
But I believe that even those, who have been persuaded . . . to observe the legal dispensation along with their confession of God in Christ, shall probably be saved. And I hold, further, that such as have confessed and known this man to be Christ, yet who have gone back from some cause to the legal dispensation, and have denied that this man is Christ, and have not repented before death, shall by no means be saved. Further, I hold that those of the seed of Abraham who live according to the law, and do not believe in this Christ before death, shall likewise not be saved [Justin Martyr, Dialogue Of Justin 47]
Didache, A.D.140 -
“Watch for your life’s sake. Let not your lamps be quenched, nor your loins unloosed; but be ye ready, for ye know not the hour in which our Lord cometh. But often shall ye come together, seeking the things which are befitting to your souls: for the whole time of your faith will not profit you, if ye be not made perfect in the last time.
Hermas - Shepherd of Hermas - Didache, A.D.140 -
They only who fear the Lord and keep His commandments have life with God; but as to those who keep not His commandments, there is no life in them. [Shepherd of Hermas, 2.7]
For the Lord has sworn by His glory, in regard to His elect, that if any one of them sin after a certain day which has been fixed, he will not be saved. For the repentance of the righteous has limits. Filled up are the days of repentance to all the saints. But to the unbeliever, repentance will be possible even to the last day… For the Lord has sworn by His Son, that those who denied their Lord have abandoned their life to despair.
And he said, “If you do not guard yourself against [anger], you and your house lose all hope of salvation . . . [Hermas. Pastor of Hermas. Book 1.4.1.]
“Hear now,” said he, “how wicked is the action of anger, and in what way it overthrows the servants of God by its action, and turns them from righteousness. But [anger] does not turn away those who are full of faith, nor does it act on them, for the power of the Lord is with them. [Book 1-2, Commandment Fourth, Chap. 1.]
Irenaeus - A.D. 156-180
“Christ shall not die again in behalf of those who now commit sin, for death shall no more have dominion over Him; but the Son shall come in the glory of the Father, requiring from His stewards and dispensers the money which He had entrusted to them, with usury; and from those to whom He had given most shall He demand most. We ought not, therefore, as that presbyter remarks, to be puffed up, nor be severe upon those of old time, but ought ourselves to fear, lest 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 be shut out from His kingdom. And therefore it was that Paul said, ‘For if [God] spared not the natural branches, [take heed] lest He also spare not thee, who, when thou wert a wild olive tree, wert grafted into the fatness of the olive tree, and wert made a partaker of its fatness.’” [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]
But with respect to obedience and doctrine we are not all the sons of God: those only are so who believe in Him and do His will. And those who do not believe, and do not obey His will, are sons and angels of the devil, because they do the works of the devil. [Against Heresies, Book 41, 2.]
Those who do not obey Him, but being disinherited by Him, have ceased to be His sons. [Against Heresies 4.41.3]
That eternal fire has been prepared for him as he apostatized from God of his own free-will, and likewise for all who unrepentant continue in the apostasy, he now blasphemes, by means of such men, the Lord who brings judgment [upon him] as being already condemned, and imputes the guilt of his apostasy to his Maker, not to his own voluntary disposition.” (Justin Martyr, fragment in Irenaeus’ Against Heresies, 5:26:1)
Tertullian - A.D. 150-220 -
1 John 2:19 - But what if a bishop, if a deacon, if a widow, if a virgin, if a doctor, if even a martyr, have fallen from the rule (of faith), will heresies on that account appear to possess the truth? Do we prove the faith by the persons, or the persons by the faith? No one is wise, no one is faithful, no one excels in dignity, but the Christian; and no one is a Christian but he who perseveres even to the end. [Tertullian, The Prescription Against Heretics, Chap 3.]
But the world returned unto sin; in which point baptism would ill be compared to the deluge. And so it is destined to fire; just as the man too is, who after baptism renews his sins: so that this also ought to be accepted as a sign for our admonition. [Tertullian, On Repentance, 2.9]
For do not many afterwards fall out of [grace]? Is not this gift taken away from many? But some think as if God were under a necessity of bestowing even on the unworthy, what He has engaged (to give); and they turn His liberality into slavery. But if it is of necessity that God grants us the symbol of death, then He does so unwillingly. But who permits a gift to be permanently retained which he has granted unwillingly? Is not this gift taken away from many?” [On Repentance, Ch. 6]
God had foreseen that faith even after baptism would be endangered. 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.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.” [- 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]
Clement of Alexandria, A.D. 195 -
He who hopes for everlasting rest knows also that the entrance to it is toilsome and narrow. So let him who has once received the gospel not turn back.
God gives forgiveness of past sins. However, as to future sins, each one procures this for himself. He does this by repenting, by condemning past deeds, and by begging the Father to blot them out. Clement of Alexandria, A.D. 195
And then there was AUGUSTINE = Catholicism & Calvin