Sorry I missed this thread when it was originally posted. Fwiw, some patristic quotes/info I originally posted here
may be of some interest:
In my own experience I have never been told that I could only pray for Orthodox Christians, or only for those who repented before they passed away. As for 1 John 5:16-17, I did a mini-study on that passage a few years back, and I found that there were multiple interpretations of the passage among the Fathers. Fwiw, here are the results of my mini-study...
Clement of Alexandria taught that there are "differences of sin". According to him, "Mistake is a sin contrary to calculation; and voluntary sin is crime; and crime is voluntary wickedness... Mistake is the involuntary action of another towards me, while a crime alone is voluntary, whether my act or another's." Clement says that 1 Jn. 5:16-17 "manifestly teaches the differences of sins" (Stromata, 2, 15)
According to St. Ambrose of Milan, we cannot take the words of this passage in a woodenly literal way. St. Ambrose believes that St. John was not saying that there were people who really couldn't be prayed for, but only that some people's sin(s) are so terrible that we sinners are unworthy to pray for them. The meaning of the passage then would be that it would take the powerful and effective prayers of a very righteous man for certain sins to be forgiven (cf James 5:16). Thus St. Ambrose says:
"Rightly, then, is it said: 'Who shall entreat for him?' It implies that it must be such an one as Moses to offer himself for those who sin, or such as Jeremiah... Such intercessors, then, must be sought for after very grievous sins, for if any ordinary persons pray they are not heard. So that point of yours will have no weight, which you take from the Epistle of John, where he says: 'He who knows that his brother sinneth a sin not unto death, let him ask, and God will give him life, because he sinned not unto death. There is a sin unto death: not concerning it do I say, let him ask.' (1 Jn. 5:16) He was not speaking to Moses and Jeremiah, but to the people, who must seek another intercessor for their sins; the people, for whom it is sufficient they entreat God for their lighter faults, and consider that pardon for weightier sins must be reserved for the prayers of the just. For how could John say that graver sins should not be prayed for, when he had read that Moses prayed and obtained his request, where there had been wilful casting off of faith, and knew that Jeremiah also had entreated?
How could John say that we should not pray for the sin unto death, who himself in the Apocalypse wrote the message to the angel of the Church of Pergamos? 'Thou hast there those that hold the doctrine of Balaam, who taught Balac to put a stumbling-block before the children of Israel, to eat things sacrificed unto idols, and to commit fornication. So hast thou also them that hold the doctrines of the Nicolaitans. Repent likewise, or else I will come to thee quickly.' (Rev. 2:14-16) Do you see that the same God Who requires repentance promises forgiveness? And then He says: 'He that hath ears let him hear what the Spirit saith to the churches: To him that overcometh will I give to eat of the hidden manna.' (Rev. 2:17) Did not John himself know that Stephen prayed for his persecutors, who had not been able even to listen to the Name of Christ, when he said of those very men by whom he was being stoned: 'Lord, lay not this sin to their charge'? (Acts 7:60) And we see the result of this prayer in the case of the Apostle, for Paul, who kept the garments of those who were stoning Stephen, not long after became an apostle by the grace of God, having before been a persecutor." - St. Ambrose of Milan, Two Books Concerning Repentance, 1, 10
Similar to St. Ambrose, St. Jerome also believes that we must not take this verse in a woodenly literal way. According to St. Jerome, St. John was exaggerating in 1 John 5:16-17 so as to emphasise that some sins could receive forgiveness easier than other sins. St. Jerome therefore seems to agree with the interpretation of St. Ambrose, but looks at what this interpretation means from a slightly different perspective. He says:
"If you cut off a finger, or the tip of the ear, there is indeed pain, but the loss is not so great, nor is the disfigurement attended by so much pain as it would be were you to take out the eyes, mutilate the nose, or saw through a bone. Some members we can dispense with and yet live: without others life is an impossibility. Some offences are light, some heavy. It is one thing to owe ten thousand talents, another to owe a farthing. We shall have to give account of the idle word no less than of adultery; but it is not the same thing to be put to the blush, and to be put upon the rack, to grow red in the face and to ensure lasting torment. Do you think I am merely expressing my own views?Hear what the Apostle John says: 'He who knows that his brother sinneth a sin not unto death, let him ask, and he shall give him life, even to him that sinneth not unto death. But he that hath sinned unto death, who shall pray for him?' (1 John 5:16) You observe that if we entreat for smaller offences, we obtain pardon: if for greater ones, it is difficult to obtain our request: and that there is a great difference between sins. And so with respect to the people of Israel who had sinned a sin unto death, it is said to Jeremiah: 'Pray not thou for this people, neither entreat for them, and do not withstand me, for I will not hear thee.' (Jer. 7:16)" - St. Jerome, Against Jovinianus, 2, 30
In his interpretation of this passage, St. Augustine focuses on the fact that St. John is in 1 John 5:16-17 speaking of a "brother" of ours: in other words, someone in the Church:
"Nor can the question in hand be solved, unless we acknowledge that there are certain sins in brethren which are more heinous than the persecution of enemies... Hence I am of opinion that the sin of a brother is unto death, when any one, after coming to the knowledge of God through the grace of our Lord Jesus Christ, makes an assault on the brotherhood, and is impelled by the fires of envy to oppose that grace itself by which he is reconciled to God. But the sin is not unto death, if any one has not withdrawn his love from a brother, but through some infirmity of disposition has failed to perform the incumbent duties of brotherhood. And on this account our Lord also on the cross says, 'Father, forgive them; for they know not what they do:' (Lk. 23:34) for, not yet having become partakers of the grace of the Holy Spirit, they had not yet entered the fellowship of the holy brotherhood. And the blessed Stephen in the Acts of the Apostles prays for those by whom he is being stoned, (Acts 7:60) because they had not yet believed on Christ, and were not fighting against that common grace.
And the Apostle Paul on this account, I believe, does not pray for Alexander, because he was already a brother, and had sinned unto death, viz. by making an assault on the brotherhood through envy. But for those who had not broken off their love, but had given way through fear, he prays that they may bepardoned. For thus he expresses it: 'Alexander the coppersmith did me much evil: the Lord will reward him according to his works. Of whom be thou ware also; for he hath greatlywithstood our words.' Then he adds for whom he prays, thus expressing it: 'At my first defence no man stood with me, but all men forsook me: I pray God that it may not be laid to their charge.' (2 Tim. 4:14-16)" - St. Augustine, Explanation of the Sermon on the Mount, 1, 22