Because man comprehends not in his knowledge or power all past and future things
 John Locke, An Essay Concerning Human Understanding (1689). copy citation

Context

“And therefore, though we cannot conceive any duration without succession, nor can put it together in our thoughts that any being does NOW exist to-morrow, or possess at once more than the present moment of duration; yet we can conceive the eternal duration of the Almighty far different from that of man, or any other finite being. Because man comprehends not in his knowledge or power all past and future things: his thoughts are but of yesterday, and he knows not what to-morrow will bring forth. What is once past he can never recall; and what is yet to come he cannot make present. What I say of man, I say of all finite beings;” source