What is nothing is at last sacred but the integrity of your own mind?

It is a quote by Ralph Waldo Emerson in his essay Self-Reliance.

Many explanations are found online that vary widely and I am by no means an expert, but here's what I gathered from the rest of the piece. The integrity of your own mind refers to making decisions without being afraid of how it will influence another's opinion of you (not too fond of society it seems); the sacred part refers to this ability (of making decision with integrity) being an important one.