Plainchant developed principally for use in

Plainchant developed principally for use in services of worship.

Explanation:

Since the very beginning of the religion of Christianity, 'chanting' has been a part of the methods of practicing and manifesting faith. These chants, as the Western and the Eastern Orthodox Churches started emerging, were started to be used to construct plainsongs called 'plainchants' to make the practice of chanting more melodious and pleasant. This practice of playing plainchants is limited to only a few churches.

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