Why do Sikhs wear a turban?
"Around your neck is a rosary, and on your forehead is a sacred mark; upon your head is a turban, and you wear two loin cloths. If you knew the nature of God, you would know that all of these beliefs and rituals are in vain." (SGGS p470)
Reply: A person who believes that any symbol or for that matter any ritual will bring them closer to God is living in deception; that is the message being conveyed by Guru Nanak here. The Guru tells us that symbols like a rosary, a sacred mark, a turban; or loin clothes do not bring one closer to God as the Brahmin had believed.
Similarly, any article of faith of any religion does not in itself bring one closer to God but the symbol may assist the person to remember God and that is the essence and aim of Sikhi and of most other faiths - "to remember God at all times". So for a Christian, wearing a Cross may help the person remember Christ and so God, and in so doing the person may tread on a true path; this is the benefit of wearing these symbols. They act as memory aids to remind us to follow the way of our Gurus or spiritual teachers.
However, the Brahmins began to believe that the symbols and rituals in themselves were the path to salvation. In this text, the Guru has not only explained to and educated the Brahmins but, in this passage, has also provided guidance on this important issue for everyone.
So the lesson to learn from this is not to think of these symbols as the 'ticket to heaven'; the symbol is only a memo to yourself to remember to book that ticket. However, you can only purchase this ticket by reciting, remembering and comprehending Naam or God; if you remember the Lord and tread on His path then you will be able to purchase the ticket to heaven! So the only way to get any spiritual benefit is by positive actions and good deeds; not by wearing X or Y or Z symbols OR by doing A, B or C rituals.
I hope this helps you to understand the concept behind religious symbols and rituals. The symbols and rituals do not provide the ultimate key to salvation but are a helping aid to keep us on the right path to obtain 'salvation'.