A Scale is a collection of pitches that work together in order to achieve some melodic-harmonic purpose. There are many kinds of melodic-harmonic purposes; there are many kinds of scales.
Each scale type has a unique personality. Each scale sounds different. More important, each scale feels different.
Each note in a scale has a particular musical function. Some establish the tonality. Some create harmonic tension. Some provide harmonic release.
Think of each scale as a distinctive palette of musical colors that work together to create a certain mood or feeling. Never think of a scale as un-bendable or un-breakable rule.