The "Do Re Mi" notation is known as the solfège system, which is a method for teaching sight-singing, where each note is assigned a specific syllable. This system was developed in the 11th century by a Benedictine monk named Guido of Arezzo. Guido wanted to improve the way music was taught and so he invented a system where specific pitches were matched with specific syllables. This system was later modified and evolved into the "Do Re Mi" system, which is still widely used in music education today.
The Origins of Music - The Story of Guido - Music History Crash Course
“When You Come Together” (1 Cor 14:26)