Musar על שבת 311:12

This explains why the Midianites brought their קסמים, enchantments, with them before setting out on their mission to Bileam (22,7). The purpose of these enchantments is to call down to earth the influence that various horoscopic constellations exert on our fates. Balak was superior to Bileam in that field. The significance of נחשים, on the other hand is, that they are instruments which deny that G–d has an entourage who act as His agents. Neither of these devices would prove harmful to Israel as long as the latter carried out the will of their Father in Heaven. The Jewish people's fate is not governed by the forces of nature, i.e. מזל. Horoscopes are something that G–d granted the nations in lieu of השגחה פרטית, G–d's personal supervision and intervention in our affairs. All other magic devices are quite ineffective against Israel as long as Israel are on the level of דביקות לה', "cleaving to G–d." The Talmud in Chullin 7, relates that a woman tried to remove some earth from under the feet of Rabbi Chaninah. Rabbi Chaninah told her to go ahead, that it would not help her to perform her magic since it is written in Deut. 4,35: "there is no one beside Him." How can this be? Do we not have a statement by Rabbi Yochanan who said that the reason sorcery is called כשפים, is because it is a denial of the forces of G–d! The Talmud answers that the case of Rabbi Chaninah is special, because he had so many personal merits that protected him. So far the Talmud on the subject. Concerning the above, Bileam said: "There is no נחש in Jacob, i.e. it is powerless against Jacob, and there is no a קסם that prevails against Israel (Numbers 23,23). Bileam was well versed in all these disciplines including his remarkable awareness of how G–d operates. He knew when to make a curse effective and draw forth G–ds wrath on someone. This is why he commenced by employing instruments of sanctity such as the building of seven altars, offering sacrifices on them, etc. He built as many altars in one single day as the patriarchs had built in their combined life times, as Rashi points out on 23,4. When he realized that G–d had not become angry at Israel and that his accusations had proved futile, he resorted to magic: הוא הלך לקראת נחשים, he forsook the approach via the sacred and turned to the profane. His attitude was that he would mention Israel's shortcomings regardless of whether G–d would react to this negatively or not. He hoped that the curse would attach itself to the mention of their sins (Rashi). Bileam abandoned recourse to the נחשים only from 24,1 onwards. He had become afraid that the merits of Israel were too great, hence he turned his attention towards the "desert," i.e. he recalled the sin of the golden calf which Israel had made in the desert and from the consequences of which G–d had saved it. When the Torah writes “ותהי עליו רוח אלוקים,” this refers to the Divine spirit resting on Israel, not on Bileam, see Zohar on 24,2.

Keeping this in mind, we can reconcile two apparently totally contradictory opinions among our sages. Some sages claim that the fortunes of the Jewish people are not subject to מזל, horoscopic influences, whereas other sages state that horoscopic influences do have a bearing on our fate (Shabbat 156a). Israel is subject to horoscopic influences. Sometimes G–d interferes and substitutes someone else for Israel. This "substitute" then experiences what would have been the destiny of Israel had G–d not interfered.