Paul in his letter to the Corinthians regards himself as the servant of Christ. Like all good servants he feels an obligation to carry out his duty justly and with a clear conscience. The duty is to dispense the truths that God has revealed. These truths are the 'mysteries of God' and they cannot be discovered by human reason alone - people must be initiated into the knowledge of them. Jesus came to initiate us into these mysteries and Paul, though a Pharisee, was initiated into this knowledge after Jesus' Resurrection on his way to Damascus.
Some of the Pharisees of Jesus' time were opposed to the teachings of Jesus. Hence, the disciples of the Pharisees wondered why Jesus' disciples were enjoying themselves in their master's company, why they were not fasting as good disciples should. After all, the Pharisees fasted twice a week.
Jesus responds to this mean talk with the image of a wedding feast. In Palestine, the wedding celebrations lasted a week, and the guests were exempted from observing any fasts during the time of celebration. At a wedding, fasting would not only be an odd attitude, it would also be rude to the hosts and other guests.
Jesus who teaches the mysteries of God, tells them that with His coming the old way has passed away: now is the time for new wine, for new vitality, for new rejoicing
Lord, give us this new vitality, may I too be eager to live the life of Jesus with a clear conscience as Paul did.