Fasting was a normal part of a godly disciplined life in the days of Jesus.  It showed the need to repent for sin, and be utterly dependent in prayer (Esther 4:3; Esther 4:16).  However, it easily became a proud religious rite (Matthew 6:16-18).  God seeks repentant people with broken hearts rather than religious people with artificially gloomy faces.  Joel 2:12-13 says, "'Even now,' declares the Lord, 'return to me with all your heart, with fasting and weeping and mourning.' Rend your heart and not your garments. Return to the Lord your God, for he is gracious and compassionate, slow to anger and abounding in love, and he relents from sending calamity."

Religious trainees fasted as part of their discipline, but Jesus' disciples did not fast.  That attracted criticism.  How could they be godly if they spent their time, going with Jesus from one meal to another, as they talked about God's kingdom with individuals, families and groups of people?  Jesus said that nobody fasts at a wedding - it is a celebratory feast.  He then likened Himself to a bridegroom surrounded by the men who were rejoicing at His wedding.  

That is why Paul described the church as the bride of Christ (Ephesians 5:25-33).  Jesus is gathering His very own special people to be His bride (Revelation 21:2).  However, in His ministry He repeatedly reminded the disciples that He would be taken away from them ... hence the reference to their mourning and sadness which became reality for them when He was crucified and buried.

Since His resurrection and ascension, Christ is with us and His Holy Spirit is in us - we rejoice that we belong to Him.  However, we are also sad and mourn over our sins - the offence we bring to Him as we disobey His commands.  But that will not last for ever.  One day we will see Him face to face and will be set free from the habit of sinning: we will be like Him (1 John 3:2).  So, until then, we live in the tension of rejoicing that we are loved as His Bride, and yet mourning over our sin.  Until we see Him in heaven, spiritual disciplines of repentance and praise are still necessary - not to earn favour with God but to recognise our dependence on Him and draw on His grace.