Why was it important, in each experiment, for redi and pasteur to have a vial that was completely closed off to the environment? *?

Redi and Pasteur were both trying to disprove the hypothesis of spontaneous generation that stated that a living organism can emerge from inorganic matter or dead flesh. Therefore, it was essential for their research to completely seal their vials and prevent contamination with living things and spores from the environment in order to prove that living things do not emerge spontaneously.