The highest subject of study is metaphysics or theology, the knowledge of God (_cf._ below, p. 285). This is not merely not forbidden in the Bible, but it is directly commanded. When Moses says, "That I may know thee, to the end that I may find grace in thy sight" (Exod. 33, 13), he intimates that only he finds favor with God who knows him, and not merely who fasts and prays.[254] Besides, the commandment, "Thou shalt love the Lord thy God," cannot be fulfilled without a study and understanding of the whole of nature.[255] Thus, as we shall see, it is only by a study of physics that we come to understand that affection is a defect and must therefore be removed from the conception of God. The same thing applies to the ideas of potentiality and actuality. We should not know what they signify without a study of physics, nor should we understand that potentiality is a defect and hence not to be found in God. It is therefore a duty to study both physics and metaphysics for a true knowledge of God.[256] At the same time we must recognize that human reason has a limit and that there are matters which are beyond its ken. Not to realize this and to deny what has not been proved impossible is dangerous, and may lead a man astray after the imagination and the evil desires which quench the light of the intellect. And it is this the Bible and the Rabbis had in mind in such passages as, "Hast thou found honey? eat so much as is sufficient for thee; lest thou be filled therewith, and vomit it" (Prov. 25, 16); or in the following from the Mishna, "Whoever pries into four things, had better not come into the world, _viz._, what is above and what is below, what was before and what will be after" (Hagigah, ch. 2). The meaning is not, as some fools think, that the Rabbis forbid the use of the reason entirely to reach what is in its power. It is _abuse_ of the reason that they prohibit, and neglect of the truth that the human reason has a limit.[257]