You will weep and mourn, but your grief will become joy. Jesus was definitely referring to his impending death and resurrection when he addressed the above remark to his disciples. Jesus knew only too well the effect that his arrest, persecution and death would have upon his followers. He was aware of the “thin” depth of their faith and commitment to the cause of their movement. He was aware of how such a “shallow” faith can easily be overwhelmed in the face of a challenge such as dealing with Jesus’ departure. Consequently, Jesus wanted to use the little time that they still had to encourage them to stay the cause by assuring them that good will ultimately overcome evil. He knew that his persecution and death will fill the disciples with grief. The only fact of which the disciples were not yet aware is that after three days, he would rise from the dead and appear to them, something that will definitely turn their grief into joy.
In the verses that immediately follow today’s passage, Jesus likens the experience that the disciples will undergo to the birthing experience (cf. John 16:21). Just as the joy experienced at the sight of a new life makes a mother forget the distress of her labor pains, so will it be with the disciples. The sight of a resurrected Jesus will make the disciples forget the events that preceded Jesus’ rising from the dead. But I also believe that the resulting joy that Jesus was talking about was to arise from the vindication that Jesus’ resurrection from the dead would occasion. For although Jesus’ death was seen as the end of the new order that Jesus was proclaiming, his rising from the dead proved it otherwise. What was seen as the last nail in the coffin of pessimism (“we had hoped that he would be the one to redeem Israel” cf. Luke 24:21) was turned into an occasion for songs of thanksgiving and praise (Responsorial Psalm of today). 
It is the death and resurrection of Jesus that we remember each time we gather for a Eucharistic service. It is what was seen as the beginning of the end that has become an occasion for recalling the wonders that God has continually wrought on our behalf. In the death of Jesus Christ, God has scored a vital victory, the salvation of men and women (the will of God is that all come to the knowledge of salvation [cf. I Tim 2:4]). It is in the death of Jesus that we are reunited with God. It is this that becomes the cause of our joy as we see the good that was hidden in the death of Jesus Christ come to light.