From the very first the church has baptized;
And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. For the promise is for you and for your children and for all who are far off, everyone whom the Lord our God calls to himself.” And with many other words he bore witness and continued to exhort them, saying, “Save yourselves from this crooked generation.” So those who received his word were baptized, and there were added that day about three thousand souls.
(Act 2:38-41 ESV)
The book of Acts is loaded with references to baptisms. About 3000 people were baptized on the original day of Pentecost. The book of Acts also enumerates the baptisms of Philip, Simon, Saul, Lydia, the household of Cornelius, Apollos, and Crispus along with many Corinthians. Not that that there aren’t discussions and arguments over baptism, but we will discuss that in other articles. (See Baptism, Universally Accepted, Widely Disputed for more about that.) For now we will just focus on core Christian beliefs that seem to be taught by everyone in Christianity.
All Christian theologians point to this same verse in the book of Romans as to the meaning of baptism.
We were buried therefore with him through baptism unto death: that like as Christ was raised from the dead through the glory of the Father, so we also might walk in newness of life. Rom 6:4ASV
All groups say that baptism is being buried with Christ, and being raised with him in newness of life, just as the words in the book of Romans say here. This is the core teaching of the meaning of baptism, right out of the letter of Paul the apostle to the Romans.
There are a few other nuggets that Paul incorporates into his epistles.
For in one Spirit we were all baptized into one body—Jews or Greeks, slaves or free—and all were made to drink of one Spirit. (1Co 12:13 ESV)
In baptism we become a part of the body of Christ which is the whole group of believers who partake of that Holy Spirit that is given to each of us and that we share.
For as many of you as were baptized into Christ have put on Christ. (Gal 3:27 ESV)
When we are baptized we are changed. We no longer are just earthly creatures, animals who can talk and reason. In baptism we are clothed with Christ, giving us access to the Father and to the power that Jesus Christ made available by dying for us on the cross.
Still, there are exceptions to the practice of baptism, the Salvation Army and the Quakers. See (Neither Baptism Nor Communion Services for Quakers and the Salvation Army for more on this.)
Again, there are numerous points of contention on the details, but for now, let’s just celebrate this area of commonality, that in baptism we were buried with Christ unto death, and raised again with him in newness of life.