The crowd doesn't understand what he's talking about, can't grasp the logic of it. even when they hear a voice from heaven, they give differing explanations.
Jesus responds to them rather indirectly. The ruler of the world is going to be ousted. Yet, Jesus adds that he himself is to be lifted up from the earth. They don't see the logic in this, either.
Note that the phrase, lifted up, has a double meaning. Jesus will physically be lifted up onto the cross. And he will be exalted.
Also note that when he is lifted up, Jesus will draw all people to himself. All.
Reading ahead: In verses 35-36, He responds rather cryptically again by talking about light and darkness. In their commentary, John, Gail R. O'Day and Susan E. Hylen remind us of the other times in this gospel that this imagery has been used to characterize Jesus and his ministry and the response of others to it: 1:4-9; 3:9-21; 8:12; 9:4-5; 11:9-10.
In this gospel, Jesus will no longer speak to the crowds but only to his disciples.