Rashi: He meant that Yisrael deserve to be blessed because they do not harbor diviners and sorcerers.

Ramban: He meant that Hashem's B'rachos are bound to materialize, seeing as Yisrael do not harbor diviners and sorcerers.

Seforno: He meant that the reason that Hashem took Yisrael out of Egypt and gave them the strength of a Re'em is because they seek Hashem and do not indulge in sorcery.

Rashbam: He meant that Yisrael are not diviners and sorcerers like they (Bil'am and Balak) are, nor do they consult Ov and Yid'oni (like they do)'

Da'as Zekenim and Hadar Zekenim: "Nachash" is an expression of testing; the Targum of "Nichashti" (Bereishis 30:27) is 'Naseisi', Do not test if He will curse them, because surely, He will not do so. And if you will say that He will not curse them, but one can harm them through sorcery ? "ve'Lo Kesem be'Yisrael", it does not work against them, because Hashem guards them.

Oznayim la'Torah: He meant that all Balak's divinations - to pinpoint the best location for his (Bil'am's) curses to take effect were futile, since Yisrael, who did not divine, were not subject to divinations.

Rashi #1: He meant that there will come a time such as this ¹ when their closeness to Hashem will be revealed, when they sit before Him studying Torah and the angels will ask them what G-d has done. ²

Rashi #2, Rashbam and Seforno: He meant that, whenever they need to know what Hakadosh-Baruch-Hu has decreed (or to know what will happen some time in the future - Rashbam) they have access to the information by means of the prophets (or the Urim ve'Tumim - Rashi). ³

Ramban: Since Balak sent for him to perform sorcery against Yisrael, Bil'am is now stating that neither divination nor sorcery are effective on Yisrael, whether for good or for bad, because both good and bad come on Yisrael directly from Hashem. ⁴

Targum Yonasan: At this (Da'as Zekenim, Hadar Zekenim - at a future) time it will be told to Yisrael how praiseworthy are the miracles and the wonders that Hashem performed for them. ⁵

Oznayim la'Torah: Refer to 23:23:1:6. He meant that Yisrael do not currently ⁶ need diviners, since all that Hashem does is revealed to them via prophets.

Ramban: Refer to 23:23:2:3.

Nedarim, 32a: Anyone who does not indulge in divination, will be brought within the boundaries of the Shechinah. ¹

Kol Eliyahu, Divrei Eliyahu: Just like one who prays for someone must mention his name, also one who wants to harm through Nichush and Kishuf. He could not mention all six hundred thousand individual names, so he chose Ya'akov, the choice of the Avos, from whom came the Shevatim ? "Arah Li Ya'akov." All his preparations and seven altars did not help at all - Ki Lo Nachash be'Ya'akov. He thought that he used the wrong name ? "Lo Ya'akov Ye'amer Od Shemecha ki-Im Yisrael" (Bereishis 32:29). He repeated all his preparations and seven altars for the Kesem against 'Yisrael', and again it did not work - ve'Lo Kesem be'Yisrael. He concluded that it is because both names apply (the name Ya'akov was not negated- only it became secondary ? B'rachos 13a). He said, now I will repeat everything against both names - ka'Eis Ye'amer le'Ya'akov u'le'Yisrael. He suspected that even this might not work; perhaps their real name is Eil ? "va'Yikra Lo Eil Elokei Yisrael" (Bereishis 33:20) - Hashem called Ya'akov 'Eil' (Megilah 18a). However, he cannot do Kesem against Eil, since it is a name of Hashem ? "Mah Pa'al Keil"!