In response to the statement of Jesus that it is impossible for the rich to enter the kingdom of God, Peter states that they as disciples have left everything to follow Jesus. The response of Jesus is a reassurance that what they have given up will be replaced by the new bond that they will share with each other both in this life and in the life to come. It must also be noted that the Marcan Jesus also mentions persecutions as being part of the lot of the disciples. These are to be expected by anyone who is a true witness of the Gospel. The last verse of this pericope speaks about the reversal of status that will be part of the kingdom indicating that that the values of the world do not apply in the kingdom.
When we sacrifice something for a cause we must realise that our reward must be the sacrifice itself. The reason why we sacrifice is because we believe in the cause, whether it is helping the poor, reaching out to the needy or any other and we must gain our satisfaction from the understanding that someone has lived more fully because of the sacrifice that we have made rather than expect yet another reward.