Why the Holy Communion must use the unleavened bread and unleavened fresh grape juice without any additives

1,Holy Communion cannot have yeast. We must use unleavened bread and break it after giving thanks.

Therefore let us keep the Festival, not with the old bread leavened with malice and wickedness, but with the unleavened bread of sincerity and truth. (1 Corinthians 5:8 )

2, The Passover Feast cannot have yeast. In new covenant, Holy Communion is the Passover Feast.

In the first month you are to eat bread made without yeast, from the evening of the fourteenth day until the evening of the twenty-first day. For seven days no yeast is to be found in your houses. And anyone, whether foreigner or native-born, who eats anything with yeast in it must be cut off from the community of Israel. (Exodus 12:18-19)

3, Holy Communion is one of the ways given by Jesus for the forgiveness sins. We need the way Holy Communion which is the one received from God.If we receive It in an worthy manner, the sins would be forgiven. If we receive it in an unworthy manner, we eat our sins.It means Whoever receives Holy Communion in an worthy manner their sins would be forgiven. Holy Communion has blood so it can forgive sins. Therefore, it must have no yeast.

For whenever you eat this bread and drink this cup, you proclaim the Lord’s death until he comes. So then, whoever eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of sinning against the body and blood of the Lord. Everyone ought to examine themselves before they eat of the bread and drink from the cup. For those who eat and drink without discern-ing the body of Christ eat and drink judgment on themselves. (1 Corinthians 11:26-29 )