I have been discipling a new Christian and he comes up with some goodies! He has asked, “What is significant about the three days of Christ's death, burial, and resurrection?” Is the fact that there are three days and not two or four meaningful? Also, what was He doing during those days? That is, was he preaching to the spirits in prison as in 1 Peter?
The answer to your second question can be found in two previous questions and answers entitled, “Where in the Bible are we told that Jesus descended into hell?” and “Where in the Bible does it speak of Jesus going to hell/hades after His death?”
The answer to your first question is unknown. Scripture never gives us that answer. So we do not know why Jesus was buried “three days and three nights.”
For as Jonah was three days and three nights in the belly of a huge fish, so the Son of Man will be three days and three nights in the heart of the earth. (NIV) Matt. 12:40
It is interesting to note that forensic science says that after death rigor mortis sets in within 2 to 13 hours. The difference in time depends on the circumstances. Putrefaction of the body begins to occur after 36 to 72 hours. This would have been common knowledge to the people of Jesus’ time.
So Jesus’ body would have been stiff and rigid and decay should have started to occur by Sunday morning. How does a putrefying body with rigor mortis sit up and walk away? It is not possible. It is not possible for Jesus to have returned to life on Sunday morning unless a real miracle occurred.
Our God wanted us to know that a miracle occurred. Jesus’ human body was already decaying when the miracle of life returned. Is that the reason for three days? It could be. We really do not know, because the scriptures never tell us and it is best that we do not assume that we know the answer.