Old habits, the temptations of sin, can become all-encompassing and all-corrupting. If we do not expel shameful wants from our mind, if we cannot resist the temptations and earthly desires of the world which will ultimately lead us to sin, our old ways (even the smallest detail) will keep us from the fullness of life we seek with Christ.
Paul sent this letter because he had heard rumors that the Corinthian community was not only splitting into various factions, but also indulging in immoral activities. Like Jesus, Paul used the images of leavened and unleavened bread to impress upon the church the dangers of allowing even one instance of immorality to influence the entire community. He compared such instances of sin to “old yeast”, and that he considered them to be threats to the entire community’s connection to Christ. He firmly believed that it is Christ who must always provide the life pattern for believers.
Paul presented Jesus as the Passover lamb in this reading. Like Christ, we as Christians must live in his transformed life, dying to the “old yeast” of immorality and sin, and live with the “unleavened bread” of the righteous path that Jesus set out for us.