why Sikh keep hair what is the use why we cutt out nail why not hair or bread etc

Respected Jasbir Singh ji,
Waheguru ji ka Khalsa, Waheguru ji ki Fateh!

In Sikhism, the Five Ks (ਪੰਜ ਕਕਾਰ Pañj Kakār) are: kesh (unshorn hair), kangha (a comb for the kesh, usually wooden), kara (a bracelet, usually made of iron or steel), kachera (a white undergarment), and kirpan (a small sword of any size, shape or metal.
The Five Ks are not just symbols, but articles of faith that collectively form the external identity and the Khalsa devotee’s commitment to the Sikh rehni, ‘Sikh way of life’. A Sikh who has taken Pahul is required to keep all five the five Ks, being the command of Tenth Guru Person, Guru Gobind Singh Sahib.

The dastār is our Guru’s gift to us. It is how we crown ourselves as the Singhs and Kaurs, who sit on the throne of commitment, to our own higher consciousness. For men and women alike, this projective identity conveys royalty, grace, and uniqueness. It is a signal to others that we live in the image of Infinity and are dedicated to serving all. The turban doesn’t represent anything except complete commitment. When you choose to stand out by tying your dastār, you stand fearlessly as one single person standing out from six billion people. It is a most outstanding act.

Further, please be kind to read the following Pangti of Shabad of Fifth Guru Person, Guru Arjun Sahib, in Raag Maru, which is located at Panna 1083-84 of Guru Granth Sahib:-

ਨਾਪਾਕ ਪਾਕੁ ਕਰਿ ਹਦੂਰਿ ਹਦੀਸਾ ਸਾਬਤ ਸੂਰਤਿ ਦਸਤਾਰ ਸਿਰਾ ॥੧੨॥ {ਪੰਨਾ 1084}

ਪਦ ਅਰਥ: ਸਾਬਤ ਸੂਰਤਿ = (ਸੁੰਨਤਿ, ਲਬਾਂ ਕੱਟਣ ਆਦਿਕ ਦੀ ਸ਼ਰਹ ਨਾਹ ਕਰ ਕੇ) ਸਰੀਰ ਨੂੰ ਜਿਉਂ ਕਾ ਤਿਉਂ ਰੱਖਣਾ। ਦਸਤਾਰ ਸਿਰਾ = ਸਿਰ ਉਤੇ ਦਸਤਾਰ (ਦਾ ਕਾਰਨ ਬਣਦੀ ਹੈ) , ਇੱਜ਼ਤ-ਆਦਰ ਦਾ ਵਸੀਲਾ ਹੈ।12।

ਅਰਥ: (ਸੁੰਨਤਿ, ਲਬਾਂ ਕਟਾਣ ਆਦਿਕ ਸ਼ਰਹ ਨੂੰ ਛੱਡ ਕੇ) ਆਪਣੀ ਸ਼ਕਲ ਨੂੰ ਜਿਉਂ ਕਾ ਤਿਉਂ ਰੱਖ = ਇਹ (ਲੋਕ ਪਰਲੋਕ ਵਿਚ) ਇੱਜ਼ਤ-ਆਦਰ ਪ੍ਰਾਪਤ ਕਰਨ ਦਾ ਵਸੀਲਾ ਬਣ ਜਾਂਦਾ ਹੈ।12।

In this Guru Sahib is teaching that one is not to disturb the appearance (ਸਰੂਪ) given by Akalpurakh. Rather, keeping it as it is a way to get respect. Therefore, one has to first get convinced about remaining in Akalpurakh’s Hukam and maintaining the Sikhi Saroop.

Now coming to cutting nails, the logical argument is that the nails when they grow beyond fingertips will accumulate dirt underneath them and (imagine eating food with same hand ) can cause health issues. The part of the nail beyond finger tip is dead and hence need to be cut.

Now about dead hair, the same also get removed when we comb our hair. However, cutting live hair (Kesh) amounts to fighting throughout one’s life with Akalpurakh, because the Kesh will continue to grow daily. Therefore, it is upto a person to remain in peace or continue the fight with Akalpurakh all through the life. One has to make a choice.

Hope it helps. If you have any further questions, please do ask. If there are any shortcomings please do point out the same for improvement in future.

Regards,
Your Brother