14 Wherefore let us most firmly hold that which faith, resting on authority established beyond all question, maintains: “that Christ died according to the Scriptures,” and that “He was buried,” and that “He rose again the third day according to the Scriptures,” and all other things which have been written concerning Him in records fully demonstrated to be true. Among these doctrines we include the doctrine that He was in hell, and, having loosed the pains of hell, in which it was impossible for Him to be holden, from which also He is with good ground believed to have loosed and delivered whom He would, He took again to Himself that body which He had left on the cross, and which had been laid in the tomb. These things, I say, let us firmly hold; but as to the question propounded by you from the words of the Apostle Peter, since you now perceive the difficulties which I find in it, and since other difficulties may possibly be found if the subject be more carefully studied, let us continue to investigate it, whether by applying our own thoughts to the subject, or by asking the opinion of any one whom it may be becoming and possible to consult.
15. Consider, however, I pray you, whether all that the Apostle Peter says concerning spirits shut up in prison, who were unbelieving in the days of Noah, may not after all have been written without any reference to hell, but rather to those times the typical character of which he has transferred to the present time. For that transaction had been typical of future events, so that those who do not believe the gospel in our age, when the Church is being built up in all nations, may be understood to be like those who did not believe in that age while the ark was a preparing; also, that those who have believed and are saved by baptism may be compared to those who at that time, being in the ark, were saved by water; wherefore he says, “So baptism by a like figure saves you.” Let us therefore interpret the rest of the statements concerning them that believed not so as to harmonise with the analogy of the figure, and refuse to entertain the thought that the gospel was once preached, or is even to this hour being preached in hell in order to make men believe and be delivered from its pains, as if a Church had been established there as well as on earth.
16. Those who have inferred from the words, “He preached to the spirits in prison,” that Peter held the opinion which perplexes you, seem to me to have been drawn to this interpretation by imagining that the term “spirits” could not be applied to designate souls which were at that time still in the bodies of men, and which, being shut up in the darkness of ignorance, were, so to speak, “in prison,”— a prison such as that from which the Psalmist sought deliverance in the prayer, “Bring my soul out of prison, that I may praise Your name;” which is in another place called the “shadow of death,” from which deliverance was granted, not certainly in hell, but in this world, to those of whom it is written, “They that dwell in the land of the shadow of death, upon them has the light shined.” But to the men of Noah's time the gospel was preached in vain, because they believed not when God's long suffering waited for them during the many years in which the ark was being built (for the building of the ark was itself in a certain sense a preaching of mercy); even as now men similar to them are unbelieving, who, to use the same figure, are shut up in the darkness of ignorance as in a prison, beholding in vain the Church which is being built up throughout the world, while judgment is impending, as the flood was by which at that time all the unbelieving perished; for the Lord says: “As it was in the days of Noah, so shall it be also in the days of the Son of man; they did eat, they drank, they married wives, they were given in marriage, until the day that Noah entered into the ark, and the flood came and destroyed them all.” But because that transaction was also a type of a future event, that flood was a type both of baptism to believers and of destruction to unbelievers, as in that figure in which, not by a transaction but by words, two things are predicted concerning Christ, when He is represented in Scripture as a stone which was destined to be both to unbelievers a stone of stumbling, and to believers a foundation-stone. Occasionally, however, also in the same figure, whether it be in the form of a typical event or of a parable, two things are used to represent one, as believers were represented both by the timbers of which the ark was built and by the eight souls saved in the ark, and as in the gospel similitude of the sheepfold Christ is both the shepherd and the door.
Source: Letters (New Advent)