Role of Khalsa

Khalsa was the military wing of the Panth. Guru Gobind Singh Ji created it to defend the Panth. Khalsa, in time of Guru Gobind Singh, was a very small percentage of the whole Panth as is the number of military is in any country compared to its population.
But to check the growing influence of Arya Samaj into Sikhism, the Singh Sabha movement introduced many changes in Sikh traditions and cut down many of its Hindu connections. One of the most important was that only a man who wears turban and keeps unshorn hair can be a Sikh, but this was not so in time of Guru Gobind Singh Ji and neither was this Guru ji's intention. He believed and preached "Manush Ki Zaat Sabe Eko pehchanbo"
Only physically fit with aptitude for fighting and killing the enemy joined the army. Neither Bhai Kanhaya nor Bhai Nand Lal had this aptitude. One could not hurt anybody, the other was a literary man, but to the Guru they were as good Sikhs as anyone else.
The role of the Khalsa in time of Guru Gobind Singh was predominantly warfare and those who did not join the Khalsa fauj were to look after Sikhs shrines, families of the Khalsa soldiers and carry on literary pursuits, just the normal civilian life.