"On the Sabbath they rested according to the commandment."
This does not seem like the proper response after your rabbi, master and lord has just been executed for a crime he did not commit. If I was one of the disciples I would most certainly freaking out right now, despite Jesus' multiple proclamations that this is exactly what was going to happen (see Luke 9:18-22). In my mind, Jesus was going to be established as king, overthrow Rome, and usher a new Golden Age of Israel. He was definitely NOT going to die by the hands of these very same Romans. But isn't it interesting that the one full day Jesus lay dead in a tomb just happened to be the Sabbath?
Now, the Sabbath is all about rest. In Genesis, God makes everything in six days, and on the seventh He rests. God does not need to rest. God is not tired after a full work week. God is doing something here. He is intentionally wiring the world to work in a certain way, a certain rhythm. God wants creation to enter a rhythm of work and rest, work and rest. The Sabbath teaches us not to rely on ourselves but to trust in God by resting in His work for us.
So then why is Jesus in the ground on the Sabbath? Because he has finished his work and now it is time to rest in that work. That is what God does. Jesus as the eternal God already has a track record of resting after a magnificent work; first in creation, and secondly in salvation. But Jesus does not need to rest after the work of the cross. The rest is for us. We are the ones that need to rest in God's work. If the disciples actually listened to Jesus and understood what was taking place, then they would be resting in the fact that God has finished His redemptive work and wait for Jesus to rise from death. But instead they had lost all hope that Jesus was who he said he was. Luke 24:21 accounts two disciples reaction to the whole scenario, "We had hoped that he was the one to redeem Israel." I can just hear the despair in their voices; "we had hoped..." I'm quite sure that although God had planned to have the death of Jesus land on a Sabbath, the disciples did not grasp the full reality of this move. For them the Sabbath was a routine part of life, and so the deep truth of this Sabbath must have been lost on them. Maybe it's just me, but I think that the reason God puts so much weight and emphasis on the Sabbath was for this specific day. Every command of God is not just a command in itself, but always points to a bigger reality. The entirety of existence in a sense is packed into 3 days. On Good Friday God works in a magnificent display of glory, He rests on the Sabbath, and then He ushers in a new creation. God's intent in the Sabbath falling between the cross and resurrection is to teach us to rest in God's work for us, trusting in his atoning work and looking forward to his resurrecting power. And notice that he is not "suggesting" we rest, he is commanding it. "On the Sabbath they rested according to the commandment (emphasis mine). Our command is not to impress God in our work, but to be impressed by His work and rest in that.
So if we take this passage and zoom out to see all of redemptive history, it would seem that we are living in the longest Sabbath ever. we live between Good Friday (God's magnificent work) and Easter Sunday (His new creation). The whole life of a Christian is one long Sabbath; we behold the work of God on our behalf, live our lives in light of that work, not adding to it, and we wait for Him to resurrect everything. So behold the marvelous atoning work of Jesus, rest in it, and wait in hope for the New Creation.