In its earliest days, the Church faced severe persecution. It was necessary for Christians to be well instructed in the faith because they may be called to defend it with their very lives. In our present culture, this depth of formation remains necessary.
Christianity is much more than “head knowledge” of certain beliefs. Being Christian must also affect one’s entire life, way of thinking, way of acting, way of praying, etc. To allow Christianity to sink in and take root requires both instruction and conversion… and conversion often takes time.