After being made alive, he went and made proclamation to the imprisoned spirits — to those who were disobedient long ago when God waited patiently in the days of Noah while the ark was being built. 1 Peter 3:18-20a NIV
Traditionally, Holy Saturday has been associated with Christ's descent into hell (descensus Christi ad Inferos). While we wouldn't push the temporal link too strongly, since Scripture only says that Christ visited the imprisoned spirits "after being made alive", yet Holy Saturday seems a good time to ponder this article of faith which has often been argued against by contemporary theologians.
"Before Christ arose and ascended into heaven, and while yet lying in the grave,
He also descended into hell in order to deliver also us from it, who were to be
held in it as prisoners ... However I shall not discuss this article in a
profound and subtle manner, as to how it was done or what it means to 'descend
into hell', but adhere to the simplest meaning conveyed by these words, as we
must represent it to children and uneducated people...since we cannot but
conceive thoughts and images of what is presented to us in words, and unable to
think of or understand anything without such images, it is appropriate and right
that we view it literally, just as it is painted, that He descends with the
banner, shattering and destroying the gates of hell...we ought ... simply to fix
and fasten our hearts and thoughts on the words of the Creed,which says: I
believe in the Lord Jesus Christ, the Son of God,dead, buried, and descended
into hell,' that is, in the entire person,God and man, with body and soul,
undivided,'born of the Virgin, suffered died, and buried'; in like manner I must
not divide it here either, but believe and say that the same Christ, God and man
in one person, descended into hell..."
From Martin Luther's Torgau
sermon on Christ's Descent Into Hell
"...we believe simply that the entire person, God and human being, descended to Hell after his burial, conquered the devil, destroyed the power of Hell, and took from the devil all his power."
Formula of Concord, Solid Declaration, Art. IX
Pic: From an altar reredos at All Souls College Chapel in Oxford, England
Note that the reredos depicts Adam and Eve alongside what appear to be other OT figures, reflecting the common but erroneous folk belief that Christ preached to OT believers in hell. This is not consistent with the Biblical sedes doctrinae (seat of the doctrine), 1 Peter 3:18f, which specifically mentions Christ proclaiming his victory to those who were disobedient "in the days of Noah".
In the history of interpretation of this passage, Augustine took the view that Christ preached through Noah to the unbelievers who later became "the spirits in prison" while Aquinas interpreted the passage allegorically, asserting that it was intended to teach simply the victory of Christ over the devil.
Other medieval interpreters thought hell was the mythological underworld, divided into various compartments for the just and unjust, the former becoming known as "the limbo of the fathers", which was liberated by Christ.
The Roman Catholic apologist Robert Bellarmine thought the spirits in prison were the souls in purgatory - an outstanding example of eisegesis or the reading into the text of information which is not there.
Lutheran interpreters through the centuries have consistently followed Luther's lead in the Torgau sermon (which also proves he did not believe in "soul sleep") and interpreted the text literally (see Bo Reicke, The Disobedient Spirits and Christian Baptism, 1946), regarding Christ's preaching as a proclamation not of forgiveness but of his victory over sin, death and the devil, a victory which meant that the condemned state of the souls in prison was confirmed.
One must be alert in our time to interpretations which favour an apocatastasis or restoration of the souls in hell - a "second chance" to hear the Gospel and repent after death which finally results in an empty hell, save for the devil and the evil angels. This view is present not only among liberal Protestants but in the Roman Catholic and Easter Orthodox churches (see here). We dare not go against the clear word of God, which tells us that people "are destined to die once, and after that to face judgment" (Hebrews 9:27).