We can see very clearly what Mark has omitted by looking at the Apostles Creed
Friday Suffered under Pontius Pilate; was crucified, dead and buried.
Saturday He descended into hell.
Sunday The third day he rose again from the dead.
The descent into hell is not to the later Christian place of eternal punishment, but the Jewish Sheol, the afterlife place of non-existence, the grave writ large. What is the meaning of that event?
As Mark set out to describe Jesus' execution he was working within Jewish tradition that had always emphasised how God vindicated those righteous Jews who remained faithful under persecution and were ready, if necessary, to die as martyrs for their faith in God. In the Apocryphal book of Wisdom we read But the souls of the righteous are in the hand of God and no torment will ever touch them. In the eyes of the foolish they seemed to have died, and their departure was thought to be a disaster, and their going from us to be a destruction; but they are at peace. For though in the sight of others they were punished, their hope is full of immortality. (3.1-4) It is such theology which is behind the gospel stories of Jesus death and vindication. First Jesus is mocked by passers by, by the authorities, and even by those crucified with him for the lack of preemptive divine intervention to save him from death on the cross.
Then we recall future vindication from several places in Mark's text. Apart from three prophecies of death by execution and vindication by resurrection in 8.31, 9.31 and 10.33-34, the promise of vindication is repeated in 13.26, They will see the Son of Man coming in clouds with great power and glory, and again in 14.62, You will see the Son of Man at the right hand of the Power and coming with the clouds of heaven. This is post-death public vindication which was in accordance with the scriptures for all who knew their tradition.
Scholars have debated whether that divine salvation refers to the immortality of the soul or the resurrection of the body. If, as in Biblical tradition, your faith tells you that this world belongs to and is ruled by a just divinity and your experience tells you that that the world belongs to and is ruled by an unjust humanity, eschatology becomes almost inevitable as the reconciliation of faith and experience. God, you believe, will transform this world of violence and injustice into one of nonviolence and justice. God will act - indeed must act - to make new and holy a world grown old in evil.
Eschatology is absolutely not about the end of this world, but rather about the end of this world's subjection to to evil and impurity, injustice, violence and oppression. It is not about the evacuation of earth for God's heaven, but about the divine transfiguration of God's earth.
How then did the claim of general bodily resurrection, surely the most counter intuitive idea imaginable, become part of that scenario of cosmic transfiguration? The general reason was because the renewal of an all-good creation here below upon this earth demanded it. How could you have a renewed creation without renewed bodies? That magnificent vision of a transformed flesh as well as as a renewed spirit, demanded transfigured bodies as well as perfect souls.
The specific reason for bodily resurrection became part of the scenario was related to martyrdom, particularly in the 160s BC in the Seleucid persecutions. The question was not about their survival but about God's justice when faced specifically with the battered, tortured and executed bodies of martyrs. Many of those who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt. (Daniel 12.2)
Those general and specific reasons had come together in apocalyptic eschatology and Pharisaic theology at the time of Jesus. When God's great cleansing happened the first order of business was the general resurrection. Since God's purpose was to establish a just and non-violent world, it had to deal with the past before it could deal with the future and there was already a great backlog of injustice that had to be redeemed, a great crowd of martyrs who had to be vindicated.
If you believed as Jesus did and as Mark wrote, that the Kingdom of God was already here on earth, you were claiming that God's great cleansing had already started, then the bodily resurrection and vindication could indeed begin with Jesus at the head of those others who had died unjustly, or at least righteously before him. This is what Jesus' descent into hell was all about. That is what Jesus had to do on Holy Saturday.