Waheguru ji ka khalsa
Waheguru ji ki fateh
At the time of tenth Guru ji there used to be three kinds of sikhs. A granth named 'Sau Sakhi' written by one Sahib Singh who claims to be a scribe to write the text of this granth as dictated by Bhai Gurbax Singh earlier known as Bhai Ram Kanwar or Ram Kaur a descendant of Baba Budha ji and a knowledgable and honoured member of Guru Gobind Singh ji''s retinue.
In the 61st Sakhi of this Granth in the 7th couplet Guru ji is said to say,
"ਤੀਨ ਪਰਕਾਰ ਮਮ ਸਿਖ ਕੇ ਸਹਜੀ ਚਰਨੀ ਖੰਡ"
Teen parkar mum sikh ke sehaji charani Khand.
There are three kinds of my sikhs, Sehaji, Charani, and Khand.
Sehaji in the present usage means Sehajdhari.
Charani means a person who became a sikh of the Sikh Gurus by receiving 'Charan Pahul or Charanamrit'. That is be drinking water in which Sikh Guru ji dipped the toe. Finally,
'Khand' means a Sikh who received the Khanda Pahul, ie baptism by drinking the water sanctified by stirring with a Khanda or double-edged sword.
It means that during later period of tenth Guru ji there was a situation when there existed Sikhs who had taken Khande di Pahul. Also there were still those sikhs around who had not taken Khande di Pahul but had earlier become Sikh by being baptised by the earlier tradition of 'CharanAmrit'. Some of them had even taken Charanamrit from ninth Guru ji. Still there were those aroung who were part of the Guruji Sangat who had neither Khande di Pahul nor Charanmrit but still considered themselves to be Sikhs of Guru ji. The later Guru calls in the above line as 'Sehaji' or Sehajdhari.
The term Sehajdhari was a borrowing from the tradition of Sidhs and Yogis.
We are aware that the traditional Buddhism during earlier centuries of CE split into Hinyan (the lower vehicle) Budhists and Mahayan (the higher vehicle) Budhists. The later evolved into Vajaryan (the diamond vehicle) Budhistrs during the eighth or ninth centuries. The follower of Vajaryan were known as Sidhs or Vajaryani Sidhs. These Sidhs adopted physical methods of meditation that came to be known as Hathyoga. Hathyoga meant very severe yogic practices or Hath meaning stubborn persistence. The leader of these Sidhs, eighty four in number, was Machhinder Nath. Machhinder Nath had a very promising and popular disciple named Gorakh Nath who split from the mainstream Sidh tradition of Vajaryan and developed a new Panth called Sehajyan (the easy or tranquil vehicle). Gorakh Nath condemed the Hath Yoga of his predecessors and advocated 'Sehaj Yog'. Sehaj Yog emphasised the training and controlling the mind rather than the severe discipline of the body in Hath Yog. The new insignia of the Sehaj Yogi was wearing a pair of thick ivory or glass rings in the ears. This resulted in them to be called 'Kanphate Yogis' or 'Yogis with pierced ears'. In Gurbani we find various Yogis in conversation with Guru Nanak Dev ji. They were followers of Gorakh Nath (who lived during ninth tenth century, but the followers who succeeded Gorakh Nath as Guru were also called Gorakh Nath as the ten Guru ji in Gurbani write their name as Nanak in Gurbani). We find the current succesor at the time of Guru Nanak also known as Gorakhnath.
'Sehajdhari' does not mean who is endeavouring slowly to become an Amritdhari as is currently being interpreted but a Sikh who does not adopt the discipline of an Amritdhari (just as Sehajyogis did not adopt the discipline of Hat Yogi Sidhs of Vajaryan) and may not ever adopt this discipline. Even after 1699 Sehajdhari Sangats in some parts of India who were entirely non-Amritdhari and Guru ji wrote them letters addressing them as 'Tusi mera Khalsa ho'. (See hukamnamey, Ganda Singh, hukamnama 55, 57, 60 )