Culturally, during Guru Nanak’s time, there was a strong caste system in place. Guru Nanak taught and gave the experience of the Almighty God openly to all people, rather than a chosen few in a special priestly caste. He taught a practical way of living, rather than a philosophy, because he said “Truth is high, but higher still is truthful living.”
Guru Nanak Dev Ji stressed on honesty and equality, saying he did not recognize caste, and he elevated the status of women. These concepts were highly revolutionary during his times. Nanak taught these values simply by practicing them.
~Resource: Living Reality by Bibiji Inderjit Kaur Khalsa.