Must someone be baptisted to join a church?
There is a very delicate balance that we must maintain here. I am once again teaching through the Book of Acts. There, you do not see anyone coming to faith without being baptized (for example the new converts in Acts 2:41; the new believers in Samaria in Acts 8:13, 16; the Ethiopian eunuch in Acts 8:36-39; Paul in Acts 9:18; those in the household of Cornelius in Acts 10:47-48). In terms of the Book of Acts it is inconceivable that one would come to faith in Christ and not be baptized.
In some countries and cultures today a profession of faith is not taken seriously apart from baptism. (It is at one's baptism that persecutionbegins.)
In the Book of Romans, chapter 6, Paul reasons on the basis of a baptism he assumes has taken place. (I understand him to be speaking of water baptism as the symbol of our spirit baptism at the time of our salvation.) The assumption is that believers have been baptized, and thus he argues that the death to sin and resurrection to new life in Christ which was symbolized at one's baptism should now be lived out by no longer living in sin, but living righteously, through the power of God's Spirit (instruction on this divine enablement comes later, in Romans 8).
While holding to the necessity of baptism as an act of obedience (Matthew 28:18-20, underscored and reinforced by the example and practice of the apostles as we see in the Book of Acts), we must also be on guard against making baptism the means of salvation (thus Titus 3:4-7; see also Paul's teaching on circumcision in Romans 2, 4, and Galatians).
I can understand why a church would be hesitant to accept a person into its membership if they have refused to obey the teaching of our Lord (Matthew 28:19), the command of the apostles (Acts 2:38), and the practice of the early church.
In our church we would not place anyone in a leadership role (Sunday school teacher, elder, deacon) if they had not been baptized.
It is probably true that in our times the need for baptism has not been emphasized enough. Perhaps this is in reaction to those who have insisted that baptism is necessary for salvation.
Also, we should also take 1 Corinthians 12:13 into account:
13 For we were all baptized by one Spirit into one body-whether Jews or Greeks, slave or free-and we were all given the one Spirit to drink (1 Corinthians 12:13).
Here, the Spirit baptism does seem to join us to the church ("one body"), as well as to identify us with Christ and His saving work. If water baptism is a symbol of our Spirit baptism, then one might see why it is required for membership in a local church.
I think the main question I would ask anyone is "Why not be baptized?"