Matthew 28:19-20. Jesus said, "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you." So here Jesus says to first make disciples and then baptize them. And so as Anabaptist, in fact, I think pretty well all Christians, by the time you get to the second century, you do see that they had an emphasis on making somebody a disciple before they baptized them.
They had probably witnessed too many people who responded suddenly to an invitation, got baptized, and then returned to the world. So they wanted to make sure this is a disciple of Jesus that we're baptizing. I'm just saying it's one reason why we take a bit of time, and this has always been the Anabaptist practice.