What is the meaning to this Spares but the cloudy border of his base To the foiled searching of mortality?

The phrase suggests a contrast between the sparse, perhaps minimal existence of the subject and the obscured or uncertain nature of life ("cloudy border"). It implies that the subject's essence or reality is only partially revealed, leading to a struggle in understanding mortality. The "foiled searching" indicates the futile attempts to grasp the full meaning of life and death, emphasizing the complexities and ambiguities inherent in human existence.