Who is a Sikh? The literal meaning of the word Sikh is a 'disciple.' A Sikh is one who is a disciple of the Satguru. To be a disciple of the Satguru, one must completely surrender one's will and wisdom to the Will and Wisdom of the Satguru. Only then, the Satguru admits one is in his fold as a 'Sikh' and blesses him with the holy Naam. This initiation ceremony was previously referred to as the deekhya or charan pahul and has been prevalent right from the time of Sahib Sri Guru Nanak Dev Ji, as support ed by Bhai Gurdas Ji:

Gur Deekhya Lai Sikh, Sikh Sadaayaa (Var 3, Pauri 11)
One is called a Sikh only after he has been blessed with 'deekhya.

Charan Dhoe Rehraas Kar
Charnamrit Gursikhaan Pilaaayaa (Var 1, Pauri 23)
(Guru Nanak) followed the system of washing the Guru's Feet and blessing the GurSikhs with the Charan amrit (Charan-Pahul)

Sahib Sri Guru Gobind Singh Ji prescribed specific rules and regulations which must be unconditionally accepted by the candidates before they can be admitted as disciples (Sikhs). The ceremony by which the Panj Pyaras are authorized by the Satguru to admit such persons in the fold of Sikhism is partaking Khande-ki-Pahul or Amrit. Therefore, according to the Commandment of the Satguru, one can become a Sikh of the Guru only by taking Amrit. Such a person is also called an Amritdhari because he has been blessed with the holy Amrit and has, thus, become a Sikh. It is further explicit from the following couplet from Rahitnamaa of Bhai Desa Singh Ji.

Pratham Rahit Yeh Jaan, Khande-ki-Pahul Chhakey.
Soee Sikh Pardhan, Avar Naa Pahul Jo Lai.
The primary Rahit for a Sikh is to take Khande-ki-Pahul. And, only he is a great who does not accept anything else.

Generally, people do not grasp the true meaning of the terms Amritdhari and non-Amritdhari Sikhs. The phrase non-Amritdhari Sikhs is meaningless. One cannot make a comparison between them.

There is only one class of Sikhs and that class is the SIKH (Khalsa). Thus, one is either a Sikh or not a Sikh.

Now consider this point from another angle. If someone belonging to other faiths like Christianity, Islam, Judaism, Hinduism, etc., wishes conversion into Sikhism, what is he required to do?

Does he become a Sikh by merely refraining from cutting his hair and wearing a turban as Sikhs do? Obviously not. (There are a number of such people with long hair, and even wearing turbans, belonging to faiths other than Sikhism). He has necessarily to partake the holy Amrit to become a Sikh. How can, then, one become a Sikh simply because of accident of birth, without being baptized? This point has also been explicitly made clear by the Satguru himself as:

So Sikh Sakhaa Bandhap Hai Bhai,Jay Gur Ke Bhaaney Vich Aavey
Aapney Bhaaney Jo Chaley Bhai, Vichharr Chotaan Khaavey (pg 601)
Only that person is a Sikh and he is my near and dear one, who comes under the total allegiance of the Guru. As against this, one who owes allegiance only to his personal will, always remains in separation and will suffer

Clearly, therefore, being a non-Amritdhari means that one has not yet declared his total allegiance and obedience to Sahib Sri Guru Nanak Dev Ji / Sri Guru Gobind Singh Ji / Sri Guru Granth Sahib Ji as his Guru. Nor has he been blessed with the Gurmantra or Naam which is given ONLY at the time of baptism by Guru Sahib himself through the Panj Pyaras. Sahib Sri Guru Gobind Singh Ji himself put a seal on this point by bowing before the Panj Pyaras for his own baptism. Are these so-called non-Amritdhari "Sikhs" greater without being baptized?

It is thus, abundantly clear that the non-Amritdharis, even though they may claim to be Sikhs, and are also considered Sikhs politically and socially, are not Sikhs in the true sense and in the eyes of the Satguru. In Gurbani, they are referred to as (a) Nigurey; (b) Gurmantar heenus; (c) Sakat; (d) Manmukh or Vemukh, and (e) Vedeen (Faithless), etc. howsoever prominent or outstanding they may be in the social and public life of the community. Gurbani defines such terms as under:

(a) Nigurey: one who has not become disciple of the Guru.

Nigurey Ko Gat Kaaee Naahee Avgann Muthhey, Chotaan Khahee. (pg 361)
For him who is without the Guru, there is no liberation. Deluded by evil propensities, he suffers.

Satgur Bajhon Gur Nahi Koee Nigurey Kaa Hai Naao Bura (pg. 435)
Without the True Guru (i.e. Guru Nanak), there is not another Guru. And one without the Guru is known as evil.

(b) Gurmantar-heenus: One who has not been blessed with the Gurmantra (Naam).

Gurmantar-Heenus Jo Praani Dhrigant Janam Bharashtneh. Kookreh Sookreh Gardheh Kaakeh Sarpaneh Tul Khaieh (pg. 1356-1357)
One who is without the Gurmantra, is the most accursed, and contaminated is his life. He is like a dog, a swine, an ass, a crow a snake, and a blockhead.

(c) Saakat: Infidel

Saakat Suaan Kaheeyey Baho Lobhee, Baho Dunnat Mael Bhareejeypg. 1326)
The dog like infidel is said to be very avaricious and is full to the brim of evil thoughts.

Saakat Besuva Poot Ninaam (pg 1239)
The infidel is nameless like a prostitute's son.

(d) Manmukh: One who follows his own will; the egocentric.

Manmukh Oodha Kowi Hai, Na Tis Bhagat Na Naao (pg. 511)
The egocentric person (i.e. Manmukh) is like a reversed lotus and possesses neither devotion nor God's name.

Manmukil Seti Sang Karey, Muh Kalaldi Daag Lagaaey (pg. 1417)
Whosoever associates with an egoist, to his countenance attaches the stigma of blackness.

Manmukh Naam Na Jannani, Vinn Naavey Pat Jaaey... Vishta Kay Keerray Pavey Wich Vishta Se Vishta Mahe Samaaye(pg. 28)
The egocentrics know not the Naam, and without Naam lose their honor... They are worms of excrement, fall in excrement, and get absorbed in excrement.

(e) Vedeen: The faithless; the irreligious.

Choraan, Jaaran, Randiaan, Kuttaneeya Di Baan. Vedinaa Ki Dosti Vedlnaa Ka Khaann Sifti Saar Naa Jannani, Sada Vasey Saitaan (pg. 790)
It is the habit of thieves, adulterers, prostitutes, and pimps that they contract friendship with the irreligious or faithless and eat their food; they know not the worth of God's praise and Satan ever abides within them.

The above are only a few of the numerous quotations from Gurbani and are self- explanatory and need no further comment.

[Gurmat Rahit Marayda, The points of Contention, Bhai Manmohan Singh Ji]