When an adult enters the Catholic Church he makes a profession of faith, and he will not be allowed to do so unless he understands what he is professing and can do so in good faith. The RCIA process is more than education, it is also a conversion process, different of course for every individual, depending on where you are when you begin.
The rites along the way which punctuate the process are intended to strengthen, guide, and prepare the individual for initiation and the demands of living in conformity with Christ, including the very real possibility of martyrdom for the faith. the time should be not less than a year, after the initial period of inquiry, from the time the person enters the catechumenate, formally declaring his intention to prepare for initiation.
for the biblical basis for Confirmation check out the first two Chapters of Acts.