During Jesus' time fasting was done to appease God. Those with the most dedication would fast two days per week. The Pharisees fasted so that others would be impressed by their perceived dedication.

John's disciples came to Jesus and asked, “Why are we fasting when you and your disciples are feasting?” Jesus tenderly responded, “Can you make the children of the bridchamber fast when the bridegroom is with them?”  

Indeed, Jesus was with the disciples so there was no need to fast and after he went to the heaven he sent the Holy Spirit. Fasting is most appropriate when you are being tempted or persecuted and you fail to discern the presence of the Holy Spirit.  

Our own works can never buy salvation. Those who fast in hopes of justifying themselves before the Lord will be bitterly disappointed. Furthermore, legalism will never lead anyone to Christ.

We should fast in an effort to empty our lives of self. Once we have renounced self, God can make us new creatures. Christ's love will fill our hearts and our lives will be a living testimony representing Jesus.