It is a mirror of the true knowledge of the personality of Akal Purush.
Japji is actually a means of presenting the divine qualities to the seeker in pure form. It is said that Guru Nanak composed this Bani immediately after Shri Guru Nanak Dev Ji entered the river Veni and came face to face with a famine man. In the Sikh tradition, this Bani is fortunate to be the first to be composed. This composition of Guru Nanak Dev ji is considered to be the beginning and the essence of Sikh ideology. Japji literally means the inspiration to remember the name of Waheguru.
The Sikh scripture Shri Guru Granth Sahib begins with Japji.