Why did Jesus remain in the tomb three days and three nights?
Christ remained in the tomb three days and three nights to prove that His death was real, not merely an unconscious state or a trick. The duration demonstrated He was genuinely dead, so His resurrection would be a true resurrection from death.
Les explains that this is why it was three days and three nights in the tomb: to prove it was not just an unconscious state, and He did not just put on a Houdini or something like that, but He was really dead. The same reality applies to believers in the realm of old Adam: old Adam has to die, and we have to be sure he is dead. As He died, we died; as He was buried, we were buried in the mind of Christ, the mind of God. He saw us in the tomb, and that is the baptism of verse 4—being engulfed in that three-day in-the-tomb experience of Christ. In order to experience resurrection from the grave, we naturally had to go into it, but we are not going to stay there any more than Christ did; we are resurrected out of it.