"A little while and you will no longer see me, and again a little while later and you will see me." So some of his disciples said to one another, "What does this mean that he is saying to us, 'A little while and you will not see me, and again a little while and you will see me,' and 'Because I am going to the Father'?" So they said, "What is this 'little while' (of which he speaks)? We do not know what he means." Jesus knew that they wanted to ask him, so he said to them, "Are you discussing with one another what I said, 'A little while and you will not see me, and again a little while and you will see me'? Amen, amen, I say to you, you will weep and mourn, while the world rejoices; you will grieve, but your grief will become joy. (Jn 16:16-20)
Jesus was revealing the father to his disciples and so doing he was revealing himself. One of the points of revelation was about his future: where he will be and where he will go to etc. The disciples did not understand this revelation. They had listened to him many times and most of Jesus’ revelation they understood. But the present revelation they did not understand.
Jesus was talking about his going to the father. But the disciples were not understanding this. Jesus was talking about the father and the heavenly things but the disciples were understanding everything in earthly way and in relation to here and now. They were so much caught up by this world and the thoughts of the world that they found it very difficult to understand the heavenly realities and the revelation of heavenly things.
The disciples will weep and mourn because Jesus has left them in this world and this world will hate them and persecute them. The world will be rejoicing in its own way. Grief and rejoicing are also this worldly realities and expression and feelings. This worldly feelings are not for ever. They would not last longer. The grief that thie disciples feel in this world are of no importance. The true rejoicing are lasting and in fact they are from God.
