There's significant evidence that under inspiration, the book of Deuteronomy and some of the historical books were edited by Jewish scribes in Babylon into their current form (16). This so-called Deuteronomic history sought to speak specifically to the needs and weaknesses of Judah in Babylonian captivity. In our present context it's interesting to note the occurrences of the term "son / children of Belial" to describe evil people. The apostate Jewish writings speak of a figure called Beliar, a kind of personal Satan figure. However, the Hebrew Bible's use of the term Belial- note the slight difference- is significant. For according to Strong's Hebrew lexicon, "Belial" essentially means "nothing" or "failure". Wicked people were therefore sons of nothing, empty, vapid... connecting with Paul's New Testament insistence that idols / demons are in fact nothing, they are no-gods. According to the Jewish Apocryphal writings, Beliar is active in leading Israel away from obedience to the Torah. But the Hebrew Bible says nothing of this- rather does is stress that Israel are themselves guilty for their disobedience and must bear full and total responsibility for this. Many of the Qumran writings mention how Belial can influence the moral center of a human being, so that they plan evil (see 1QH-a 2.16, 22; 4.12-13; 4.12; 6.21-22; 7.3; 10.16-17; 14.21). Yet this is totally the opposite of what the Hebrew Bible (as well as the New Testament) emphasize- that the human heart itself is the source of temptations, and therefore human beings are totally responsible for their own sins.
A case could also be made that the whole record of Israel's rejection from entering the land of Canaan is framed to adduce a reason for this as the fact they chose to believe that the land was inhabited by an evil dragon who would consume them there. This was a slander of the good land, and the whole point was that if they had believed in the power of God, then whatever 'adversary' was in the land, in whatever form, was ultimately of no real power (Num. 13:32; 14:36; Dt. 1:25). And yet it was not God's way to specifically tell the people that there was no such dragon lurking in the land of Canaan- instead He worked with them according to their fears, by making the earth literally open and swallow up the apostate amongst them (Num. 16:30)- emphasizing that by doing this, He was doing "a new thing", something that had never been done before- for there was no dragon lurking in any land able to swallow up people. And throughout the prophets it is emphasized that God and not any dragon swallowed up people- "The Lord [and not any dragon] was as an enemy; He has swallowed up Israel" (Lam. 2:5 and frequently in the prophets). The people of Israel who left Egypt actually failed to inherit Canaan because they believed that it was a land who swallowed up the inhabitants of the land (Num. 13:32), relating this to the presence of giants in the land (Num. 13:33). As Joshua and Caleb pleaded with them, they needed to believe that whatever myths there were going around, God was greater than whatever mythical beast was there. And because they would not believe that, they failed to enter the land, which in type symbolized those who fail to attain that great salvation which God has prepared.
Isaiah's statement that Yahweh creates both good and evil / disaster, light and darkness, is not only aimed at criticizing the Babylonian dualistic view of the cosmos. It also has relevance to the false ideas which were developing amongst the Jews in Babylon, which would later come to term in the false view of Satan which most of Christendom later adopted. According to the Jewish Apocryphal writing The Visions of Amram, human beings choose to live under the control of one of two angels. Amram has a vision of the two opposing angels who have been given control over humanity (4Q544 frg. 1, col. 2.10–14 [Visions of Amram-b] = 4Q547 frgs. 1–2, col. 3.9–13). The good angel supposedly has power “over all the light”, whereas the evil angel has authority “over all the darkness” . Thus the idea of dualism - which is so attractive to all people- was alive and well amongst the Jews; and thus Is. 45:5-7 was also aimed at the developing Jewish belief in Babylon in a dualistic cosmos.
(1) Paul Carus, The History Of The DevilAnd The Idea Of Evil (New York: Gramercy Books, 1996) p. 58.
(2) I have exemplified this at length in Bible Lives Chapter 11.
(3) J.B. Russell, The Devil (Ithaca: Cornell University Press, 1977) p. 174.
(4) H.C. Kee, Medicine, Miracle And Magic (Cambridge: C.U.P., 1986) p. 70.
(5) Geza Vermes, Jesus The Jew (London: S.C.M., 1993) p. 61.
(11) As quoted in Umberto Cassuto, Biblical And Oriental Studies (Jerusalem: Magnes Press, 1975) Vol. 2 p. 98.
(12) Cassuto, ibid., p. 134.
(13) Cassuto, ibid. pp. 156, 164.
(14) English translation in Cassuto, ibid. pp. 206-208.
(15) Demonstrated in great detail by Umberto Cassuto, A Commentary On The Book Of Genesis (Jerusalem: Magnes Press, 1992) Vol. 2 pp. 255-259.
(16) The similarities of style, language and indications of common editing are explained in detail in Martin Noth, The Deuteronomistic History (Sheffield: JSOT Press, 1981); there is a good summary in Terrence Fretheim, Deuteronomic History (Nashville: Abingdon Press, 1989). See too M. Weinfeld, Deuteronomy And The Deuteronomic School (Oxford: Clarendon Press, 1972).