The Feast of Unleavened Bread is celebrated for a whole week, beginning the day following the Passover.
When Jesus provided deliverance from sin by his blood, God immediately provided a covering for our sins; not a condoning of sin, but a provision so we could be accepted by him.
Leaven is a type of sin, and at the festival they were to eat unleavened bread, representing sin pardoned.
Under the new covenant, leavened bread was used because God provided justification. Instead of SIN, FAULT and FAILURE, God sees, through the covering he provided, HOLINESS, BLAMELESSNESS and PERFECTION.
Colossians 1:21 And you, that were sometime alienated and enemies in your mind by wicked works, yet now hath he reconciled
22 In the body of his flesh through death, to present you holy and unblameable and unreproveable in his sight:
That is to say, that when God looks at us through the prism of Jesus' sacrifice, He does not see our sin, but the holiness of Jesus, our faults, but the blamelessness of Jesus, our abject failures, but the unreproveable perfection of Jesus. This is ours provided we stay under the covering of the atonement.
Those who choose rebellion and idolatry voluntarily move out from under his covering.
Hebrews 10:14 For by one offering he hath perfected for ever them that are sanctified.
15 Whereof the Holy Ghost also is a witness to us: for after that he had said before,
16 This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them;
17 And their sins and iniquities will I remember no more.
18 Now where remission of these is, there is no more offering for sin.
The reason for such a glorious provision is because He wants us to be able to have rich and wonderful communion with Him, to enjoy an awareness of His presence every day. He accomplishes this through His Word and Spirit.
God not only wants believers to come closer to Him; He wants those who are far away from Him to come too.
God WANTS you! He is not looking for reasons to disown you, but for reasons to help you and to bring you closer to Himself.
Isaiah 1:18 ... though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.