The Quran was revealed to the Messenger of Allah (salallahu alayhe wa sallam) with tajweed. Then the Messenger of Allah (salallahu alayhe wa sallam) taught it to his companions with tajweed, and they taught their students likewise.
Up to this day, the scholars of tajweed teach the Quran as it was taught by the Messenger (salallahu alayhe wa sallam).
Why is Tajweed Important?
The science of tajweed has preserved the exact words of the Quran and their pronounciations. This is the purpose of this science and not necessarily to recite with a beautiful voice (as is a common misconception). That's not to say that one can recite the Quran beautifully without learning tajweed.
According to the scholars of tajweed, it is obligatory (fard al-ayn) for each individual to recite with the rules of tajweed, but it is a communal obligation (fard al-kifayah) for a community to have an individual who knows the whole science with all its rules and terminologies.
The science of tajweed will be split into four parts: