Why wait two days longer instead of coming immediately unless Jesus wanted to give free reign to death before he conquered it so that no one could doubt Lazarus had truly died?
In other words, Jesus wanted to grant free reign to the grave to allow corruption to set in. He prohibits neither putrefaction nor stench from taking their normal course. He allows the realm of darkness to seize his friend, drag him down to the underworld, and take possession of him. He acts like this so that human hope may perish entirely and human despair reach its lowest depths. The deed he is about to accomplish may then clearly be seen to be the work of God, not of man.
[Jesus] waited for Lazarus to die, staying in the same place until he could tell his disciples that he was dead. Then he announced his intention of going to him. “Lazarus is dead,” he said, “and I am glad.” Was this a sign of his love for his friend? Not so. Christ was glad because their sorrow over the death of Lazarus was soon to be changed into joy at his restoration to life. “I am glad for your sake,” he said. Why for their sake? Because the death and raising of Lazarus were a perfect prefiguration of the death and resurrection of the Lord himself. What the Lord was soon to achieve in himself had already been achieved in his servant. This explains why he said to them, “I am glad for your sake not to have been there, because now you will believe.” It was necessary that Lazarus should die, so that the faith of the disciples might also rise with him from the dead.