In these instances, the word rendered adversary or adversaries, is Satan, and means nothing more than an opponent.
When the Jews were carried captives to Babylon, they came into immediate contact with a people, the Persians, who believed in a good being and a bad one. Ormazd was their good God, and Ahriman their Devil. The latter was as clearly defined in the duality of Zoroastrian theology, as the former. During their seventy years' captivity it could not be otherwise, than that the enslaved people should imbibe some of the customs and beliefs of their masters. If they went so far as to change the characters of their language from the original Hebrew letters to those of the Chaldas, it is easy to see that they would of course, adopt this notion of an evil principle and personality, so prevalent at that time in Chaldea. After the Babylonian exile the doctrine of a Devil became a part of the Jewish belief, and the evil spirit was termed Satan, as he was the foe or adversary of God. In First Chronicles 21 : 1, there is a circumstance related in which Satan or the Devil is the principal agent. The words are: "And Satan stood up against Israel and provoked David to number Israel." Now the book of Chronicles being written after the captivity, it was quite natural that the writer should consider and designate the enemy of God, the Devil or Satan. But the same event is mentioned in another of the Jewish books, written before the captivity, and the temptation of David is referred to entirely another being. Here the words are:
"And again the anger of the Lord was kindled against Israel, and moved David against them, to say, 'Go number Israel and Judah,' Thus in the earlier books, the affair is attributed to the Lord, but in the books written after the Jewish connection with the Chaldeans and Persians, Satan is blamed for the same act. This, beyond doubt proves the source of the Christian superstition respecting the Devil." ("The Devil," by John Watts.)
"With this dualistic system the Jews came in contact during their captivity at Babylon, and are supposed to have retained permanent traces of it in their subsequent theology. The conception of the Devil and of a lower kingdom of demons or devils is the evident illustration of this. (Ency. Brit. V. Devil.)