9. Some of the great Tzaddikim were obliged to go into these philosophies in order to extricate and elevate the souls that fell and became sunk in them. One cannot argue that it is permissible for others to enter these philosophies because many of the great scholars of the past were involved. … People who are not on a comparable level of sanctity – and, needless to add, the ordinary people of our own age – should never enter these realms and risk being eternally lost (Likutey Moharan I, 64:3).
10. The song of the true Tzaddik has the power to draw up the souls that have fallen into this form of atheism, from which otherwise there is no return (ibid. I, 64:5).
11. The materialist philosophers, who claim that everything operates solely by virtue of the laws of nature, are a breed of wild animals who have made terrible inroads into our people and caught many of our sons in their clutches. Many Jewish souls are sunk in this like birds caught in a snare. If you love your soul, keep well away from these wild beasts, who would otherwise snatch your soul and consume it. Keep well away from books of speculative science, even those written by our own great sages. There is no greater evil (ibid. II, 4:6).