The Bill of Rights, including the Fourth Amendment, was drawn up to alleviate the concerns of those delegates to the Constitutional Convention worried that the proposed Constitution would give too much power to the federal government. The American colonists had only recently fought a war against what they saw as British tyranny. The last thing they wanted to see was the re-establishment of such tyranny on American soil. The states, in particular, were genuinely worried that the Constitution as it originally stood would impinge upon their sovereignty. Moreover, they feared that an over-mighty federal government would infringe the individual liberties for which Americans had fought so long and hard.
The Fourth Amendment's protection against unreasonable searches and seizures has obvious relevance to the criminal justice system. In order to bring charges against individuals it will often be necessary to conduct searches of both property and person. The Fourth Amendment is there to make sure that, when such searches do take place, they are carried out in accordance with appropriate legal safeguards, such as the issuing of a warrant by a judge. This is an expression of one of the fundamental principles of American public life, that the government is a government of laws, not men. It is the law, and not the personal whims of individuals, that should determine how law enforcement officials conduct their work.
A notable anomaly of the Fourth Amendment was that it only applied to federal, not state authorities. As such, individuals were deprived of protection against unreasonable search and seizure by state officials. It was only in the middle of the 20th century that the Warren Court, in cases such as Mapp v Ohio (1961), extended Fourth Amendment rights to cover actions by the states.