No one can have access to the spiritual regions without a Master. According to the Hindu scriptures, when Narad Rishi went to Vishnu puri, abode of Lord Vishnu, he was denied admittance because he had no Master. Therefore, he had to adopt a Master.
Sukhdev, the son of Ved Vyas, was possessed of spiritual knowledge even while in his mother's womb, but when he visited Vishnu puri he was turned out because he had no Guru. He could not visit the spiritual regions, and had to adopt Raja Janaka as his Guru.
There is no instance in history that tells of any man making the spiritual ascent without a Guru.
Saints who possess knowledge from the time of their birth are rare. They do not, however, go against the tradition, and for this reason they also adopt a Guru.
Kabir Sahib, for example, adopted Gosain Rama Nand as his Guru. It is a historical fact that such Saints, although they had knowledge from the time of birth, remained in the company of Saints and derived benefit from them. Guru Amar Das said that it is ordained by the Lord from the beginning that He cannot be realized except with the help of a Guru.
It has been ordained by the Lord since the beginning; no one can know Him without a Master.
Bihagara Var M5, 556-2
This being so in the case of those who are born Saints, it follows that a Guru is all the more necessary for common people. According to tradition, even the incarnations of Lord Vishnu – Lord Rama and Lord Krishna, adopted the Rishis Vashist and Garg respectively as their Gurus. These instances are mentioned solely for our benefit. Rama and Krishna, who were Lords of the three worlds, had to obey the law; lesser men can claim no exception.
In support of this, Guru Nanak Sahib says that no one has ever had knowledge without a Guru. You can verify this truth, he says, from Brahma, or the great sages Narad and Vedvyas.
Oh brother, none but a Master can tell the secret of God-Realization. You may ask this of Brahma, Narad or Vedvyas.
Sri Rag M1, 59-7
Tulsi Sahib says:
No one is greater than Rama and Krishna; but they also had a Guru. They were the Lords of the three worlds; but they depended on the Guru.
Whoever progressed on the spiritual path did so at the instance of a Mahatma.
Ashtavakar imparted knowledge to Raja Janaka. Gorakh Nath obtained it from Bhartri Hari, Arjun from Lord Krishna and Vivekananda from Ramakrishna.
Amongst the Sikhs it was Guru Nanak who inspired the second Guru, Angad; Guru Angad inspired Guru Amar Das; Guru Amar Das inspired Ram Das; Guru Ram Das passed on the Light to Guru Arjan, and so on, till the tenth Guru, Guru Gobind Singh
Maulana Rumi says that it was Shamas-i-Tabrez who changed his life.
The man of mere learning that I was, I did not become Rum's man of God until after I became the slave of Shamas-i-Tabrez.
He again says:
Oh Master, give Maulana Rumi a kind look. I say without shame or reserve, as do Qalandars (God-intoxicated person), that I am a slave of Shamas-i-Tabrez.
Many Mahatmas have mentioned their Gurus in their hymns, while some have not done so. The principle, however, is the same. The Guru is a Light that lights another, and a Life that gives rise to another.
It is very necessary for us, who are engulfed in Maya, to obtain initiation from a True Guru.