The ordinance of the sacrament has two components, bread and wine, or at least some liquid that is represented by the cup. The New Testament model clearly shows the combination of bread and the cup in the Last Supper scenario, as well as in tradition (Paul F. Bradshaw. The Search for the Origins of Christian Worship. Oxford University Press, 2002, p. 69).
The model available for the Sacrament in the Book of Mormon is very certainly a particular instance, that of the appearance of the Savior in Bountiful, where Mormon records that the sacramental meal is introduced to the gathered Nephites. In contrast to the description on the covenant of the bread discussed in the commentary on Moroni 4, we have a less clear correspondence between the covenantal description and the prayer language given in Moroni 5 for the blessing on the wine:
3 Nephi 18:8-10
8 And it came to pass that when he said these words, he commanded his disciples that they should take of the wine of the cup and drink of it, and that they should also give unto the multitude that they might drink of it.
9 And it came to pass that they did so, and did drink of it and were filled; and they gave unto the multitude, and they did drink, and they were filled.
10 And when the disciples had done this, Jesus said unto them: Blessed are ye for this thing which ye have done, for this is fulfilling my commandments, and this doth witness unto the Father that ye are willing to do that which I have commanded you.
In Mormon’s description of the event, we still have the essential retention of the covenant of obeying the commandments. Of course that particular phrase is explicit in the blessing on the bread, but only implied by the parallel “do always remember him” that we find in the wine-blessing. The similarities and dissimilarities of the descriptive record in 3 Nephi and the proscriptive record in Moroni suggest that while the language in Moroni is fixed, it was not necessarily a repetition of a fixed phrase in the original plate record. It must be remembered that Mormon and Moroni are writing late in the Nephite practice, and both of them would be familiar with the sacramental prayers as Moroni records them. Therefore, the similarities in language that we find in the blessing on the bread have an equal chance of being influenced from Mormon/Moroni’s familiarity with the fixed-language practice as that the fixed-language was inherited from the 3 Nephi event as originally recorded.
The development of the sacrament as a liturgical form in early Old World Christianity tells us that there is a certain evolutionary development of the rite. While the base model of the sacrament is certainly the Last Supper, there is only a tenuous relationship between developed Christian practice and the Pashal nature of that Last Supper. Where the Last Supper is conducted in the context of a Passover meal, it is clear that later Christian practice was completely disassociated with the Paschal meal, even though the event retains the Passover symbolism of the salvation of mankind through the sacrifice of the Savior as a representation of the Paschal lamb. At the very least, the Christian practice is represented very early as occurring with much greater frequency than the annual Passover meal. (Paul F. Bradshaw. The Search for the Origins of Christian Worship. Oxford University Press, 2002, p. 65).
In the Book of Mormon we have room for a similar development from a form that is contextually similar to a combination of the feeding of the multitudes and the institution of the sacrament. Note the contextual presentation of the sacrament in 3 Nephi. Prior to the introduction of the sacramental symbol, there is a feeding until sated:
3 Nephi 18:1-6
1 And it came to pass that Jesus commanded his disciples that they should bring forth some bread and wine unto him.
2 And while they were gone for bread and wine, he commanded the multitude that they should sit themselves down upon the earth.
3 And when the disciples had come with bread and wine, he took of the bread and brake and blessed it; and he gave unto the disciples and commanded that they should eat.
4 And when they had eaten and were filled, he commanded that they should give unto the multitude.
5 And when the multitude had eaten and were filled, he said unto the disciples: Behold there shall one be ordained among you, and to him will I give power that he shall break bread and bless it and give it unto the people of my church, unto all those who shall believe and be baptized in my name.
6 And this shall ye always observe to do, even as I have done, even as I have broken bread and blessed it and given it unto you.
In the known available model for Nephite sacramental practice, there is the presence of the two symbolic elements, that of bread and wine. However, the original distribution is a feeding event, and the emphasis is placed on eating until each has had his fill. This would appear to parallel the early Christian practice of the agape feast during which the sacrament was presented. It would also appear that a similar parallel development occurs in the New World where the symbolic aspects of the sacrament are emphasized and codified separately from the meal, In the Book of Mormon case, this is represented by the fixed-form prayers that Moroni presents, that are not explicitly given for the 3 Nephi event.