Spinoza's answer is curious: unhappily, a fragment of his letter only is extant, so that it is too brief to be satisfactory:--
In reply to your difficulty (he says), although each particular thing be truly in the Infinite mind, conceived in Infinite modes, the Infinite idea answering to all these cannot constitute one and the same mind of any single being, but must constitute Infinite minds. No one of all these Infinite ideas has any connexion with another.
He means, we suppose, that God's mind only perceives, or can perceive, things under their Infinite expression, and that the idea of each several mode, under whatever attribute, constitutes a separate mind.
We do not know that we can add anything to this explanation; the difficulty lies in the audacious sweep of the speculation itself; we will, however, attempt an illustration, although we fear it will be to illustrate _obscurum per obscurius_. Let A B C D be four out of the Infinite number of the Divine attributes. A the attribute of mind; B the attribute of extension; C and D other attributes, the nature of which is not known to us. Now, A, as the attribute of mind, is that which perceives all which takes place under B C and D, but it is only as it exists in God that it forms the universal consciousness of all attributes at once. In its modifications it is combined separately with the modifications of each, constituting in combination with the modes of each attribute a separate being. As forming the mind of B, A perceives what takes place in B, but not what takes place in C or D. Combined with B, it forms the soul of the human body, and generally the soul of all modifications of extended substance; combined with C, it forms the soul of some other analogous being; combined with D, again of another; but the combinations are only in pairs, in which A is constant. A and B make one being, A and C another, A and D a third; but B will not combine with C, nor C with D; each attribute being, as it were, conscious only of itself. And therefore, although to those modifications of mind and extension which we call ourselves, there are corresponding modifications under C and D, and generally under each of the Infinite attributes of God, each of ourselves being in a sense Infinite--nevertheless, we neither have nor can have any knowledge of ourselves in this Infinite aspect; our actual consciousness being limited to the phenomena of sensible experience.