What do you mean by Raj karega khalsa aki reheh na koi ------ who is going to do raj?

Answer 1

Simple explanation so this phrase would be: -

"the pure shall rule, and impure will be no more"

But it didn't justify the whole Dhora so I decided to have an in depth look in to it.

Guru Gobind Singh had written Dohra at Hazoor Sahib. He wrote this Dohra after giving Gur Gaddi to Guru Granth Sahib and original text is at Hazoor Sahib and this is being read there since 10th Guru's time. This Dohra is also written in Giani Gian Singh's book and perhaps also in Biaji Mkut Sakhi 10. The Dohra is also quoted in a few Rehitnamas.

"Agya bhai Akal ki tabhi chalayo Panth Sabh Sikhan ko hukam hai Guru manyo Granth Guru Granth Ji manyo pargat Guran ki deh Jo Prabhu ko milbo chahe khoj shabad mein le Raj karega Khalsa aqi rahei na koe Khwar hoe sabh milange bache sharan Jo hoe." Translation:

"Under orders of the Immortal Being, the Panth was created. All the Sikhs are enjoined to accept the Granth as their Guru. Consider the Guru Granth as embodiment of the Gurus. Those who want to meet God, can find Him in its hymns. The pure shall rule, and impure will be no more, Those separated will unite and all the devotees shall be saved."

The composition of this sacred Granth contains rendering (Bani) of six Gurus of Sikh faith and some Bhaktas and saints. It was composed in this form in the year 1604 with the addition later of Guru Tegh Bahadur's Bani (sacred composition). And its blessings are sought by the seeker with devout heart. Sikh religion sincerely believes that in each of succeeding Gurus, the spirit of Guru Nanak was operating incarnated.

The sacred Granth is installed in all Sikh holy places of worship and treated as presiding presence of Guru, an apostle of Divine Truth. The devotees of congregation in solemn assembly pray and seek blessings of the Supreme. This comes through in the mystical thought of Gurbani and it stands for realization of the Truth. The Gurus' word, known as 'sabad' is taken as the mystic thought of Guru.

In the words of Bhai Gurdas, a great scholar of Guru's time, "In the word is the Guru, and the Guru is in the word (sabad). In other words, the human body was not the Guru but the light of the word (shabad) and within the heart was their real personality." When the human mind dives deeper and deeper into the Guru's word, all mental impurities depart and wisdom of the Guru draws on the human soul. Thereby the devotee attains the divine light and wisdom which makes him to contemplate on God's name (naam). In the light of above realities, the Sikh religion makes the holy Granth as a living master of Sikh Panth.

Before setting for heavenly abode, Sri Guru Gobind Singh, the tenth Guru, the founder of order of Khalsa brotherhood, conferred the Guruship to Sri Granth Sahib as a living Guru of Khalsa.