Hair is a characteristic feature of mammals, commonly known as "Hairy quadrupeds" - a group of animals that mark the climax of evolution. Mammals are also the dominant animals in the world today, due partly to their ability to regulate body temperature in the face of variations in environmental temperature.
Man marks the climax of evolution even among mammals, and has the most complex and highly developed brain, and the longest hair on head. This feature cannot be without reason. It cannot be a matter of mere chance or a mistake by nature, because if the tails has been lost the hair too could have been lost. On the contrary, human head-hair has increased manifold as compared to other mammals.
For a baptised or Amritdhari Sikh, it is mandatory to keep the hair or kesh uncut honouring and accepting the perfection of God's creation. This command was issued by the tenth master, Guru Gobind Singh at Vaisakhi 1699. A comb called a Kanga is also carried to keep the hair tidy, a symbol of not just accepting what God has given, but also an injunction to maintain it with grace.
There are various Shabads in the Sri Guru Granth Sahib which favour the keeping of hair.
God is Kesva
God is referred to as "Kesva" ( ਕੇਸਵ ) - "having long hair"
|ਨਿਰਹਾਰੀ ਕੇਸਵ ਨਿਰਵੈਰਾ ॥|
|Nirhĝrī kėsav nirvairĝ.|
|He does not need to eat; His Hair is Wondrous and Beautiful; He is free of hate.|
|ਸਗਲ ਪਦਾਰਥ ਅਸਟ ਸਿਧਿ ਨਾਮ ਮਹਾ ਰਸ ਮਾਹਿ ॥ ਸਪਰਸੰਨ ਭਝ ਕੇਸਵਾ ਸੇ ਜਨ ਹਰਿ ਗਣ ਗਾਹਿ ॥੪॥|
|Sagal paḝĝrath asat siḝẖ nĝm mahĝ ras mĝhi. Suparsan bẖaė kėsvĝ sė jan har guṇ gĝhi.(4)|
|All wealth, and the eight miraculous spiritual powers are in the supremely sublime essence of the Naam, the Name of the Lord.|
Those humble beings, with whom the beautifully-haired Lord is thoroughly pleased, sing the Glorious Praises of the Lord.(4)
With my Hair, I wash, fan, dust...
There are many Shabads in the Sri Guru Granth Sahib which refer to the Guru "Fanning", "washing" or "dusting" the feet of Saints, the "servants" of the Lord. To do these activities, one needs long hair as one cannot fan someone's feet with short trimmed hair (unless you use your head as a brush!)
|ਟਹਲ ਕਰਉ ਤੇਰੇ ਦਾਸ ਕੀ ਪਗ ਝਾਰਉ ਬਾਲ ॥ ਮਸਤਕ ਅਪਨਾ ਭੇਟ ਦੇਉ ਗਨ ਸਨਉ ਰਸਾਲ ॥੧॥|
|Tahal karao ṯėrė ḝĝs kī pag jẖĝrao bĝl. Masṯak apnĝ bẖėt ḝėo gun suno rasĝl.(1)|
|I perform service for Your slave, O Lord, and wipe his feet with my hair.|
I offer my head to him, and listen to the Glorious Praises of the Lord, the source of bliss.(1)
|ਕੇਸਾ ਕਾ ਕਰਿ ਬੀਜਨਾ ਸੰਤ ਚਉਰ ਢਲਾਵਉ ॥ ਸੀਸ ਨਿਹਾਰਉ ਚਰਣ ਤਲਿ ਧੂਰਿ ਮਖਿ ਲਾਵਉ ॥੧॥|
|Kėsĝ kĝ kar bījnĝ sanṯ cẖaur dẖulĝvao. Sīs nihĝrao cẖaraṇ ṯal ḝẖūr mukẖ lĝvao.(1)|
|I make my hair into a fan, and wave it over the Saint.|
I bow my head low, to touch his feet, and apply his dust to my face.(1)