1 Peter 4:6
For, for this cause—The expression, “For, for this cause,” refers to an end to be reached, or an object to be gained, or a reason why anything referred to is done. The end or reason why the thing referred to here, to wit, that “the gospel was preached to the dead,” was done, is stated in the subsequent part of the verse to have been “that they might be judged,” etc. It was with reference to this, or in order that this might be, that the gospel was preached to them.
Was the gospel preached also to them that are dead—Many, as Doddridge, Whitby, and others, understand this of those who are spiritually dead, that is, the Gentiles, and suppose that the object for which this was done was that “they might be brought to such a state of life as their carnal neighbors would look upon as a kind of condemnation and death”—Doddridge. Others have supposed that it refers to those who had suffered martyrdom in the cause of Christianity; others, that it refers to the sinners of the old world (Saurin), expressing a hope that some of them might be saved; and others, that it means that the Saviour went down and preached to those who are dead, in accordance with one of the interpretations given of 1 Pet. 3:19. It seems to me that the most natural and obvious interpretation is to refer it to those who were then dead, to whom the gospel had been preached when living, and who had become true Christians. This is the interpretation proposed by Wetstein, Rosenmüller, Bloomfield, and others. In support of this it may be said:
(1) THAT THIS IS THE NATURAL AND OBVIOUS MEANING OF THE WORD DEAD, WHICH SHOULD BE UNDERSTOOD LITERALLY, UNLESS THERE IS SOME GOOD REASON IN THE CONNECTION FOR DEPARTING FROM THE COMMON MEANING OF THE WORD.
(2) THE APOSTLE HAD JUST USED THE WORD IN THAT SENSE IN THE PREVIOUS VERSE.
(3) THIS WILL SUIT THE CONNECTION, AND ACCORD WITH THE DESIGN OF THE APOSTLE. HE WAS ADDRESSING THOSE WHO WERE SUFFERING PERSECUTION. IT WAS NATURAL, IN SUCH A CONNECTION, TO REFER TO THOSE WHO HAD DIED IN THE FAITH, AND TO SHOW, FOR THEIR ENCOURAGEMENT, THAT THOUGH THEY HAD BEEN PUT TO DEATH, YET THEY STILL LIVED TO GOD. HE THEREFORE SAYS, THAT THE DESIGN IN PUBLISHING THE GOSPEL TO THEM WAS, THAT THOUGH THEY MIGHT BE JUDGED BY PEOPLE IN THE USUAL MANNER, AND PUT TO DEATH, YET THAT IN RESPECT TO THEIR HIGHER AND NOBLER NATURE, THE SPIRIT, THEY MIGHT LIVE UNTO GOD. IT WAS NOT UNCOMMON NOR UNNATURAL FOR THE APOSTLES, IN WRITING TO THOSE WHO WERE SUFFERING PERSECUTION, TO REFER TO THOSE WHO HAD BEEN REMOVED BY DEATH, AND TO MAKE THEIR CONDITION AND EXAMPLE AN ARGUMENT FOR FIDELITY AND PERSEVERANCE. COMPARE 1 Thes 4:13; Rev. 14:13.
-- Barnes Notes on the New Testament