Faith in Christ isn't the only way peoples' lives are changed--but it is one way. In our study of the Feasts of Israel we have noted that one of the prophetic foundations of Christianity is that there will be a life-change in the person who puts his faith in the Christ. 1 Corinthians 5:8: "Let us therefore celebrate the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth" (NASB).
Here the apostle argues that the logical extension of faith in the Messiah of Israel would be the keeping of the feast with the unleavened bread of sincerity and truth. The feast he refers to is the Feast of Unleavened Bread which was a prophetic presentation of the fact that Messiah would die in order for the ones who trusted in Him to live. Thus, according to Christianity, life comes through death. This is true analogically in that the believer dies with Christ when he puts his trust in Him. It is also true physically in that heaven only follows physical death. Life comes by way of death. But the apostle, arguing that we ought to live by eating the "unleavened bread of sincerity and truth", has his focus on living.
But the verse says there are three ways to live. One is living by the old leaven. This is former religious practice. People have always been religious, but not always in a personal relationship with God. After faith in Christ, one should put aside the old religion that did not bring the relationship with God that religion is supposed to bring. Many people today are caught up in religious systems that do not bring them closer to God. Often these people actually come to faith in the Christ through the witness of someone outside their religious system. Then, though they ought to leave that sterile system, they simply claim faith in Christ and stay where they were. Paul said to celebrate the feast NOT with old leaven.
Then there is the leaven of malice and wickedness. This is anti-religious antagonism. The believer may have been an anti-religious person before he came to faith in Christ. But he is not supposed to continue to be so. Faith in Christ puts us in the Church. We should not claim to be believers and not have an active membership in a local body of believers. If we do we shall continue to eat the bread of malice and wickedness.
Then there is the unleavened bread of sincerity and truth. Not sincerity alone--that can get you killed and condemned. But with sincerity and truth. God is the author of truth and He desires all who believe in Christ to be both of the truth and sincere. Truth without sincerity is hypocrisy. Sincerity without truth is a blind alley.
Though peoples' lives are changed by many things, a commitment to Jesus Christ will change one's life in the direction of sincerity and truth. This was prophesied by the Feast of Unleavened Bread, and it is fulfilled in every person who honestly takes Jesus Christ as the way to God. When Truth (Jesus Christ) is wedded to sincerity (the believer acting in honest faith), life results. Do you eat this bread?