Man's respect for the imponderables varies according to his mental constitution and environment. Through certain modes of thought and training, it can be elevated tremendously, yet there is always a limit.

In this quote, H.P. Lovecraft, an influential writer of horror and weird fiction, reflects on the concept of respect for the imponderables, or those things beyond human comprehension or control, such as the unknown or the supernatural. He suggests that man's respect for these mysterious forces is not universal but instead is shaped by his mental constitution—his personal mindset, beliefs, and intellectual capacity—and the environment in which he exists. This highlights the role of individual perception and external influences in shaping how we view the vast, inexplicable aspects of the universe.

Lovecraft also posits that through specific modes of thought and training, a person’s capacity to respect or even understand the imponderables can be expanded. This suggests that intellectual development, exposure to different philosophies, or immersion in certain disciplines (like science or philosophy) can open up one's mind to the vast mysteries of existence. However, despite the potential for growth in respect or understanding, Lovecraft implies that there is always a limit to how much the human mind can grasp. This limit might be due to the intrinsic boundaries of human cognition or the mysteries that simply lie beyond our current understanding.

The idea that there are things we cannot fully comprehend or control is central to Lovecraft’s works, where his characters often confront terrifying entities or forces that push the boundaries of human understanding. His cosmic horror literature explores how these imponderables can destabilize one’s sense of reality and self. This quote is a reflection of that theme—our attempt to understand the vast, unknown universe is inherently constrained by the limits of our perception and knowledge.

Ultimately, Lovecraft's words serve as a reminder of the vastness and complexity of existence. Despite all the intellectual progress humanity has made, we remain small in the face of the infinite unknown, with only a limited capacity to comprehend or respect it. This tension between the desire to understand and the inevitable limits of human understanding is a central theme in Lovecraft’s worldview.