One troubling concept I hear made from time to time is something to the effect of a person being baptized into "the PCA" or the "OPC" or the "RPCNA" or the like. I have even heard people argue against Roman Catholic baptism on the basis that baptism is into a church, and that because the Roman Catholic church is not a true church, its baptism is invalid (despite being - if administered in the traditional way - formally valid).
This is wrong. Baptism is a sign of entering into the visible church of God, certainly. Nevertheless, Baptism is not a rite of denominational (or congregational) "membership."
1 Corinthians 1:13 Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul?
The answer, of course, is no. All who are properly baptized (i.e. seriously baptized with water in keeping with Scripture, specifically, Matthew 28:19) are baptized into the outward administration of the covenant of grace in the New Testament, just as all those who were circumcised were ritually brought within the outward administration of the covenant of grace in the Old Testament.
Being circumcised by a Pharisee made you (outwardly) a Jew, not outwardly a Pharisee. Likewise, being baptized makes one (outwardly) a Christian: not a Presbyterian - not a Baptist - not an Eastern Orthodox.
At least, that is how Paul's words seem - on their face - to be intended.
The invisible church, whose boundaries are determined by the operation of the Holy Spirit (pictured as washing in Baptism), is not divided. There is no "presbyterian section" and "baptist section." These divisions, as necessary as they may be, are superficial and temporary.
I also recognize that membership has an important role to play in terms of administering the new covenant decently and in good order. Nevertheless, I am concerned that far too much attention is sometimes paid to having members and wielding authority over them (and the importance of wielding authority is very real and proper), to the detriment of proselytization.
That's one of several reasons I don't widely advertise my specific denomination - not because I don't want people to join it, but because I want the focus to be on following Christ in any evangelical church - any church that preaches the gospel of Jesus Christ.