Baptism has historically been recognized as an important part of the salvation/church ritualism. Of course, the exact role of baptism has been highly debated. Some insist that baptism is essential prior to achieving salvation, and others believe that it is only required as a token of an already achieved salvation and a step necessary to affiliation with the church. Some baptize infants and small children for fear of their dying and being rejected by God due to inherited sin. Others consider children safe until some vague age of accountability and therefore don't practice infant baptism. In this regard, baptism is a perfect example of how the divine requirements for salvation are not understood and taught uniformly across Christendom.
My own personal experience involves multiple baptisms under the old paradigm of achieved salvation. Many others have related similar stories to me about their having been baptized more than once within various Christian churches.
Since Christian Orthodoxy teaches a procedure driven salvation, one in which the one being saved must participate and do so correctly, every step in that procedure must be identified and acted upon. For many that includes baptism, as noted above. Because of that, many in the church have been baptized more than once. A second or third baptism may be initiated because a childhood baptism was later determined to be invalid because of immaturity or insincerity. In other cases, some become convinced later that the method of their earlier baptism was incorrect, making it ineffective in their fulfilling God's commandments.
The fact the re-baptism is so prevalent in evangelical churches is powerful evidence of the confusion which exists in those groups about the church's salvation process. A great number of the members just aren't sure when or if they are safe from God's wrath in accordance with their church's teachings. It is a sad and woefully disconcerting state of affairs for those who adhere to the idea of escape from eternal punishment by believing, practicing, and behaving properly.
Inescapably, if I must perform in order to be acceptable to God, I need a clear understanding of the requirements and an unmistakable verification of when I have been accepted. None of that remotely exists within Christian Orthodoxy, and the resultant anxiety is everywhere evident in our churches. Each re-baptism attests to the underlying and completely inevitable uncertainty of salvation by me.