The Body of Christ
The body of Christ is a group of Christians, not a single individual, who have a relationship with Jesus Christ. The Bible says that Jesus is the "Rock", the One who holds all things together. He has taught us that all men are created equal and that we should love one another. When we are loving and accepting of each other, we become the body of Christ.
Paul's teaching on the body of Christ is a bit more complicated than a typical sermon. Its origin is unclear, but the concept is likely to have been developed in later letters.
Among other things, Paul compared the church to a body. He claimed that believers are unified with Jesus in his heavenly kingdom. However, he did not explain how or when that union occurred.
He also used an image to explain how Christians were joined together. The image might have been meaningful to Jews and Gentiles alike.
One of the most important applications is the vertical relationship between believers. A key component to this idea is the Lord's Supper. Taking a piece of bread and drinking a cup of wine in the name of the Lord is equivalent to participating in the Body of Christ.
Another is the Golden Rule. When we do things for others, we will be rewarded by God.
Peter's message in Acts
The message of Peter in Acts was to emphasize the continuity between God and Jesus. He preached to an audience that was receptive to his message. But there is no evidence that all of the listeners were baptized.
Some debate the meaning of the passage. One interpretation is the "conversion-initiation" interpretation. This view holds that the audience was converted at the moment of faith. Another is the "transitional" interpretation. It holds that Peter's message in Acts regenerated the audience when they were at the moment of faith. These two interpretations attempt to account for Luke's soteriology.
However, there are numerous examples of people who were baptized but did not receive the Holy Spirit. In addition, there are many references in the Bible that contradict this interpretation. So, while some modern Evangelicals might hold to this interpretation, it is too ambiguous to be a universal guide for all believers.
Peter also identified the audiences as sons of the prophets. In doing so, he pointed to the promise of Abraham. As part of this promise, Abraham was promised that all families of the earth would be blessed. That promise was later fulfilled in the person of Christ.
John Mark's mission team in Gentile lands
John Mark's mission to the Gentile lands was an interesting if not awe inspiring experience. During his travels, he and his retinue discovered a treasure trove of information about the holy city of Jerusalem. He also managed to glean information on the state of the art in technology and culture from a variety of mummies and babes. However, his mission was hampered by his lack of formal education.
Upon his return from the foreign land, the aforementioned duo parted ways. A number of scribes were quick to point out that the title of the aforementioned paean was undeserved. Not to be deterred, John retorted with an admonition. Unlike many of his colleagues, he exhibited a willingness to learn. This was borne out in the next few years, when he enlightened his fellow travellers on the best way to conquer the sands of time. Eventually, he and Silas were given the missionary seal of approval by Peter and Paul.
Jesus Christ is the "Rock"
In Paul's first letter to the Corinthians, he asserts that Christ is the Rock. But many scholars have argued that his assertion is a departure from exegesis. Rather, he appears to be using the same premise that the Prophets, the Writings, and the Gospels all have.
Although Jesus Christ did not actually make a statement about rocks, Paul identifies him with the rock of water in the wilderness. During the long march, the Israelites were provided with life-giving water. Those who believe in Jesus will never thirst again. The Bible instructs Christians in leadership positions to continue to be faithful to Christ's teachings.
One of the things he teaches is that believers are to drink from the cup of Christ's death until he returns. This is also the same thing as a well. However, the rock of water that the Israelites drank from was not a moveable well.
It is the same for the spiritual rock of the church. In 1 Corinthians 10:4b, Paul says that Christ is the spiritual rock that the people of Israel experienced when they were in the wilderness.