We all know that leaven is yeast and how it invades the entire dough and thoroughly incorporates itself causing the whole loaf to rise or puff up. A dough cannot be both leavened and unleavened nor can it be partially leavened or unleavened. It is either leavened or unleavened.
From the Old Testament times God had instituted the feast of Unleavened Bread: “Seven days you shall eat unleavened bread; on the first day you shall put away leaven out of your houses, for if any one eats what is leavened, from the first day until the seventh day, that person shall be cut off from Israel.” __ Exodus 12:15. And a further command was also made: “You shall not offer the blood of my sacrifice with leaven . . .” __ Exodus 34:25
Then after the original Passover the people had no time to let the dough rise and therefore ate unleavened bread on their way out of Egypt toward the Holy Land. Thereafter, the feast of the unleavened bread and the Passover or Paschal Feast were forever inseparably united as a remembrance of how the Lord delivered His people from captivity and from their affliction . . . and the bread thereafter is also notably known as the Bread of Affliction.
Why is this important to God and to us? For Christ makes it clear as do the Apostles. First Christ must work with unleavened bread (without stain of sin) in order that He might leaven the ‘new man’ with the leaven of the Kingdom of Heaven: “The kingdom of heaven is like leaven which a woman took and hid in three measures of meal, till it was all leavened.” __ Matthew 13:33
Paul then forever links the ‘old leaven’ with sin (malice and evil): “Your boasting is not good. Do you not know that a little leaven leavens the whole lump? Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our paschal lamb, has been sacrificed. Let us, therefore, celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth.” __ I Corinthians 5:6-8
Since, Christ, our Paschal Lamb has been sacrificed, Paul’s reasoning seems to be linked to the command of God that, “You shall not offer the blood of my sacrifice with leaven . . .” __ Exodus 34:25. Since only unleavened bread is offered with a blood sacrifice (the Paschal Lamb) no leaven is allowed. If we are to offer ourselves up to the Lord as our sacrifice then we, too, must be unleavened so that Christ might be the ‘new leaven.’
Now Christ also goes on to warn us as follows: “Take heed and beware of the leaven of the Pharisees and Sad′ducees.” __ Matthew 16:6, before He tells the followers that He is not speaking of bread but of their teachings. Luke says something similar in chapter 12, verse 1, when he compares leaven with hypocrisy. So all of these things corrupt the whole and puff us up and make us unworthy to be put in the hand of God so that He might give to us the ‘new leaven’ which might spread out to the rest of mankind as God intends.
Chalcedon and I had a short conversation in the comments recently about leavened and unleavened bread being used in the Eastern vs. Western forms of Catholicism . . . and there is good reasoning for both traditions. However, we know that the Pasch that Jesus ate with the apostles on Holy Thursday was unleavened bread: “Now on the first day of Unleavened Bread the disciples came to Jesus, saying, ‘Where will you have us prepare for you to eat the passover?’” __ Matthew 26:17. And it is true that for some period of time the Roman Church also used leavened bread (hopefully, signifying the ‘new leaven’ of Christ). However I found this paragraph recently on New Advent:
Some authors are of the opinion that down to the tenth century both the Eastern and Western Churches used leavened bread; others maintain that unleavened bread was used from the beginning in the Western Church; still others hold that unleavened or leavened bread was used indifferently. St. Thomas (IV, Dist. xi, qu. 3) holds that, in the beginning, both in the East and West unleavened bread was used; that when the sect of the Ebonites arose, who wished that the Mosaic Law should be obligatory on all converts, leavened bread was used, and when this heresy ceased the Latins used again unleavened bread, but the Greeks retained the use of leavened bread. Leavened bread may be used in the Latin Church if after consecration the celebrant adverts to the fact that the host before him has some substantial defect, and no other than leavened bread can be procured at the time (Lehmkuhl, n. 121, 3).
So the two traditions are not likely to change.
The other topic of the Eucharistic wafer was even more significant in our discussion: though one need only see that ‘wafers’ were used in the Old Testament bread offerings to God from Exodus through I Chronicles 23:29. I might also say that the manna given in the desert was also perceived as a wafer: “Now the house of Israel called its name manna; it was like coriander seed, white, and the taste of it was like wafers made with honey.” __ Exodus 16:31. So I can see the True Manna that came down from Heaven as being the fulfillment of the first manna given to the Israelites.
Though that aside about Eucharistic breads is of little consequence in the grand scheme of things, I find it interesting nonetheless.
The importance of keeping ourselves and our Church free from the leaven of sin, wrong teaching, and hypocrisy is of the upmost urgency, it would seem to me; for it is clear that God wishes to be the one that molds the ‘new man’ (unleavened) into that which is fitting for the Kingdom of God. Christ in the Eucharist can then be our leaven and we, in turn, can be leaven to the world.