Douai Commentary...45 "With godliness"... Judas hoped that these men who died fighting for the cause of God and religion, might find mercy: either because they might be excused from mortal sin by ignorance; or might have repented of their sin, at least at their death.
46It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins.
46 "It is therefore a holy and wholesome thought to pray for the dead"... Here is an evident and undeniable proof of the practice of praying for the dead under the old law, which was then strictly observed by the Jews, and consequently could not be introduced at that time by Judas, their chief and high priest, if it had not been always their custom.
both of which are just as applicable if folks were already sent to hell but could be saved in the final judgement through the prayers of the saints (and their living relatives/aquaintances)
Context, context, context. Judas was doing a superstitious act since under the law, the idol worshipers were to be dealt with without mercy. Under the law they were not to be considered part of Israel or under the blessing of the Covenant. None of them had fallen in godliness as the verses say, so what's the point? An exercise in futility is the foundation for a doctrine? If that's the case why not create a doctrine for calling on the dead saints for help like Saul did with Samuel?
38: Then Judas assembled his army and went to the city of Adullam. As the seventh day was coming on, they purified themselves according to the custom, and they kept the sabbath there.
39: On the next day, as by that time it had become necessary, Judas and his men went to take up the bodies of the fallen and to bring them back to lie with their kinsmen in the sepulchres of their fathers.
40: Then under the tunic of every one of the dead they found sacred tokens of the idols of Jamnia, which the law forbids the Jews to wear. And it became clear to all that this was why these men had fallen.
41: So they all blessed the ways of the Lord, the righteous Judge, who reveals the things that are hidden;
42: and they turned to prayer, beseeching that the sin which had been committed might be wholly blotted out. And the noble Judas exhorted the people to keep themselves free from sin, for they had seen with their own eyes what had happened because of the sin of those who had fallen.
43: He also took up a collection, man by man, to the amount of two thousand drachmas of silver, and sent it to Jerusalem to provide for a sin offering. In doing this he acted very well and honorably, taking account of the resurrection.
44: For if he were not expecting that those who had fallen would rise again, it would have been superfluous and foolish to pray for the dead.
45: But if he was looking to the splendid reward that is laid up for those who fall asleep in godliness, it was a holy and pious thought. Therefore he made atonement for the dead, that they might be delivered from their sin.