What were the major teachings of Guru Nanak? Explain their relevance in the contemporary world.

गुरु नानक की प्रमुख शिक्षाएँ क्या थी ? समकालीन दुनिया में उनकी प्रासंगिकता की व्याख्या कीजिए । (150 words)
What were the major teachings of Guru Nanak? Explain their relevance in the contemporary world. (150 words)