The Sixth Amendment is the lengthiest of the original Ten: “In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the assistance of counsel for his defense.”
One reason why it is so lengthy is that it is so important. Most of the clauses in this amendment were long-standing pillars of English law, and the Founders naturally wanted them continued under the Bill of Rights. It was a tenet of English law for the accused to have a timely hearing, and the Founders made sure that such provision was protected under the Constitution. After all, without this guarantee, a defendant could be jailed for an inordinately lengthy period prior to his trial, a condition that has prevailed in many dictatorships and authoritarian countries as an easy way to keep opponents out of circulation without actually bringing them to trial.
The public trail provision of this Amendment is to assure that defendants are not tried in secret courts but in open, public courts. This is another protection against unfair legal proceedings, and public trials also help to prevent untruthful testimony – as is often said, “sunshine is a good disinfectant.”