Many Christians assumed that Jesus commanded the use of baptism and holy communion. But there very few New Testament references to these practices and it was argued that none of them showed any intention by Jesus that they (or any other practice) should have become fixed ceremonies.
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Hi-
It is true that the Bible is not a liturgical handbook (nor is it many other things that we sometimes would like it to be, such as a catechism or a text in systematic theology or a 2000-year-old newspaper . . . )
It’s a huge stretch, however, to suggest that the sacred text does not show any intention by Jesus that the sacraments, particularly the two you cite, become “fixed ceremonies.”
This is going to be a short answer, each piece could and has been expanded at great length.
Baptism - the Great Commandment (Matt. 28:19) “Go and make disciples of all nations, baptizing them in the name of the Father and the Son and the Holy Spirit.”
And on Pentecost Peter’s response to the inquiry “what are we to do?” answered “Repent and be baptized in the name of Jesus Christ for the forgiveness of your sins.” (Acts 2:38)
There are many more references to baptism, which make it clear that it was considered by the Apostles to be an essential act. (See Philip and the Ethiopian, or Peter at the house of Cornelius, or Ananais’ reception of Saul/Paul, just for a few.) The precise format has varied down through the ages but has always required water and the Name.
As to the Eucharist, the gospel accounts are clear that Jesus took an existing sacred ritual (*see note, below) and fulfilled it, explaining that the flesh and the blood would henceforth be His. He specifically said “when you do this” so He obviously expected them to do so. And again the book of Acts makes it clear that the Apostolic church did carry on the ritual of “breaking bread” daily (Acts 2:46, 20:11) and Paul is quite emphatic about the significance of the act and uses explicitly ritual language in his discussion in 1 Cor. 11:23-32). Again-the format of the celebration (as part of a communal meal or at the end of a teaching session, on a beach or in home or a cathedral) has varied, the essential elements (unleavened bread and wine) and the Words of Institution have not.
As further evidence (although not convincing to Scripture-only types) we have the writings of Justin Martyr in about 140-150, contemporaneous with the sorting out of the canon of Scripture, who describes the rituals of both Baptism and Eucharist and says that they celebrate as they have been taught by the Apostles.
*For those who are not familiar with the Jewish theology of the Passover, by consuming the flesh of the lambs sacrificed for Passover as the Lord had commanded Moses the faithful became part of the Exodus. By drinking of the cup “at the end of the meal” they entered into the Sinai covenant in which the Israelites were sprinkled with the blood of the sacrifices. Note that at the time of Jesus the Passover ritual included just four cups of wine, the modern ritual includes a fifth in honor of the martyrs, but at the time of Jesus the final cup was the fourth, the Cup of the Covenant.
I’m sure others will have more to add to this but hope it gives you some confidence.
