Can We Pray for Those in Mortal Sin?

If anyone sees his brother sinning, if the sin is not deadly, he should pray to God and he will give him life. This is only for those whose sin is not deadly. There is such a thing as deadly sin, about which I do not say that you should pray. (1 John 5:16)

It should be noted that the passage does not forbid praying for such a person but rather does not recommend it. We see a similar recommendation in 2 John 7-11 in which Christians are told to shun dissident preachers.

The passage in question does not seem to be telling us not to pray for run of the mill sinners who may be in mortal sin. The overwhelming testimony of Scripture and early Church tradition argue against such an interpretation. It is much more likely that the community to which this letter was addressed was undergoing a crisis involving grave heresy. To show to the early Christian community the seriousness of the heresy the persons who stubbornly persisted in such serious heresy were to be excluded completely from the community and its liturgies, a sort of ex communication.

As previously stated, this was a recommendation and not a commandment. It was also related to a very specific set of circumstances in the early Christian community. We can still pray for those who are in mortal sin today.