1st Day of Unleavened Bread
The New Testament Church observed the Days of Unleavened Bread for many years. The Apostle Paul writes to the Church at Corinth to explain that Jesus Christ is our Passover Lamb so that we may be spiritually unleavened even as we are physically unleavened. (1 Cor. 5:7-8)
The New Testament is filled with passages explaining the necessity for the Christian to put sin out of his life-to repent. Leaven is a symbol for sin.
Jesus died to pay the penalty for sins that man has committed. He is our King which means Christians are committed to obedience to Christ, our Lord. To be "unleavened" means to grow toward living as Jesus lived, a life of overcoming sin.