In part I of this paper I argue that on his theory of the mind as the idea of an actually existing body Spinoza is unable to account for the ability of the mind to have adequate knowledge, and I suggest that his theory of the eternity of the mind can be viewed as his solution to this problem. In part II I deal with the question of the meaning of ‘eternity’ in Spinoza (i.e., whether eternity involves timelessness or not, and why), in regard both to God and the human mind, and I sketch a line of thought which I believe may have provided him with further motivation for his theory that a part of the mind is eternal.