This quote by Voltaire suggests that if a person is not in tune with the trends, ideas, and beliefs of their era, they are likely to suffer the worst aspects of that era. The “spirit of his time” refers to the prevailing cultural, social, and intellectual climate of an era. To have the spirit of one’s time means to understand, engage with, and perhaps even shape these trends and ideas.

Those who lack this spirit, according to Voltaire, are destined to endure all the era’s miseries. This could mean that they’re left behind by societal progress, misunderstood or ostracized by their contemporaries, or simply unable to find happiness and fulfillment in a world that seems alien to them.

In today’s world, this quote can be interpreted in several ways. For instance, in the era of rapid technological advancement, those who fail to adapt to new technologies might find themselves at a disadvantage, struggling to keep up with the pace of change. In this context, the “misery” Voltaire speaks of could be the frustration, isolation, and missed opportunities that come from being left behind.

From a personal development perspective, the quote suggests the importance of lifelong learning and adaptability. To avoid the misery of being out of sync with one’s time, one must continually strive to understand and engage with the world around them. This might involve keeping up with new ideas and trends, learning new skills, or simply remaining open to new experiences and perspectives.

In essence, Voltaire’s quote is a reminder of the importance of staying engaged with the world, adapting to change, and striving to understand and shape the spirit of one’s time. Without this engagement, one risks being left behind, misunderstood, and ultimately, miserable.