Up to the Reformation era, church membership depended largely upon the accident of geographical location of one's birth. If you were born in a town under the authority of a Christian magisterium, or in a Christian kingdom, you were baptized as an infant, and you grew up Christian.
In contrast, Baptists contested that baptism should only be for those who profess Christ as their Lord and Savior (which infants could not). In order to belong to a Baptist church, you had to convert from your sinful ways, confess your sins, and publicly acknowledge and claim Jesus as Lord. If you did so, you demonstrated it symbolically through "Believer's Baptism."
For this reason, Baptists are evangelical. The National Association of Evangelicals provides a brief, but helpful description of Evangelicalism here. Baptist historian Prof. David Bebbington of Oxford University identifies four core characteristics of Evangelicalism that is universally applicable:
- CONVERSIONISM: the belief that lives need to be transformed through a “born-again” experience and a life long process of following Jesus.
- ACTIVISM: the expression and demonstration of the gospel in missionary and social reform efforts
- BIBLICISM: a high regard for and obedience to the Bible as the ultimate authority
- CRUCICENTRISM: a stress on the sacrifice of Jesus Christ on the cross as making possible the redemption of humanity.
All four characteristics are closely linked with the Believer's Church commitment of Baptists. Conversionism is core to a Believer's Church. Because Baptists think that conversion is necessary to come into Christ's Church, Baptists are, of course, committed to Activism. Baptists readily accept and promote Biblicism simply because it is a core commitment of the Apostolic Faith--contending for the faith passed down to the saints through the apostles as Jesus taught them. Finally, Baptist are also Crucicentric since it is Christ's sacrifice on the cross that makes conversion possible.