I heard a lengthy description of the blood covenant and communion which stated that the bread at communion represents the wheat (black and white) which is ground to make us all one people, water is the baptism, the heat represents eternal flame. I am unable to find any description of the importance to the elements of the bread (unsure if leavened or unleavened is correct) used at communion and its relationship to the blood covenant. I am also confused as to whether communion is a representation of an act i.e. celebration/commemoration or if the wine and bread actually become the blood and body of Christ.
To understand the significance and symbolism of the Lord's Supper one should have a knowledge of the Jewish Passover. It was at a Passover Seder (supper) that Jesus took wine and unleavened bread and applied them to himself. (Matthew 26:19-30; Mark 14:16-26; Luke 22:12-20; 1 Cor 11:23-31)
The Passover was instituted during the tenth (final) plague on Egypt before the exodus. To avoid the plague of the death of the firstborn, the Jews were to kill a lamb and put its blood on their doorposts. They were to eat the entire lamb that night with unleavened bread, ready to leave at a moment's notice. When the angel sent by God saw the blood on the doorposts, he passed over that house. Hence the name Passover. God told the Jews that henceforth they were to celebrate this event once a year. Among other things, they were to celebrate it with unleavened bread because they left Egypt so quickly they didn't have time for the bread to rise. (Exodus 12:39) Over the years a specific order (seder) developed for this memorial feast. Included are specific times when unleavened bread is eaten. It was at one of these times that Jesus broke the bread and instituted that part of the Lord's Supper. Also included were four specific cups of wine, the third of which is called the cup of salvation. It was when drinking this third cup that he instituted the second part of the Lord's Supper.
The Lord's Supper, therefore, consists of partaking of unleavened bread, which Jesus said represented his body, and the fruit of the vine (wine or grape juice, not water), which Jesus said represented his blood shed for remission of sins. There is no required "heat" component to the Lord's Supper. There is no water to represent baptism.
So, as relates to a covenant of blood, the fruit of the vine represents the blood shed for sin. The unleavened bread (which may be made of any of the five biblical grains: wheat, oats, barley, rye, or spelt) represents the flesh of Christ, like the offerings of lamb in the Old Covenant. "For even Christ our Passover lamb is sacrificed for us." (1 Corinthians 5:7)
For over five hundred years the Roman Catholic Church has been teaching that the bread and wine actually and miraculously became the substance of the flesh and blood after being blessed by the priest during mass. It doesn't matter that chemically they remain bread and wine. The justification for this doctrine is that Jesus said, "This is my body. This is my blood." It disregards the fact that his body had not yet been sacrificed and his blood had not yet been shed. On the other hand, Martin Luther argued that Jesus also said "I am the door," but that didn't make him a literal door. Although I believe the bread and fruit of the vine are symbolic, it really doesn't matter whether that is true, or the other. What matters, according to Paul in the passage in 1 Corinthians 11 mentioned above, is my attitude. Do I take it in a worthy manner? Am I, when partaking of the Lord's Supper, "discerning" (picturing, aware of) the body and blood of Jesus? If so, it doesn't really matter whether it turns into flesh and blood or just symbolizes them. Anything else is idle argument.