Continuing on from the last post, let us look at 1 Chronicles 9:2: "Now the first inhabitants that dwelt in their possessions in their cities were, the Israelites, the priests, Levites, and the Nethinims." It's interesting that the Israelites (those of Judah and Benjamin) are distinguished from a group called the Nethinims. Now the priests and Levites are for sure Israelites--who've been called to serve in the Tabernacle.
Going on to Ezra 2:58-59 we've got: "All the Nethinims, and the children of Solomon's servants, were three hundred ninety and two.And these were they which went up from Telmelah, Telharsa, Cherub, Addan, and Immer: but they could not shew their father's house, and their seed, whether they were of Israel..." This sheds further light on these Nethinims. And a few verses further in this passage: "61And of the children of the priests: the children of Habaiah, the children of Koz, the children of Barzillai; which took a wife of the daughters of Barzillai the Gileadite, and was called after their name: 62These sought their register among those that were reckoned by genealogy, but they were not found: therefore were they, as polluted, put from the priesthood." What is going on here? Well, we should always read a verse or a couple of verses in their context; thus this thing about these polluted priests must be connected to the Nethinims.
It appears that the Nethinims were Canaanites (therefore including Kenites) who'd been taken captive by the Israelites: "Also of the Nethinims, whom David and the princes had appointed for the service of the Levites, two hundred and twenty Nethinims: all of them were expressed by name." (Ezra 8:20) They performed the more menial work of the Levites (in the Tabernacle and in the Levite dwellings too, I suppose)--and were transfered over to the more menial service of the Temple once it had been constructed (by Solomon).
Then by the time of Ezra these Nethinims (being of Kenite extraction and being deceptive like their father, Satan) had already insinuated themselves into the priestly class--and were now being found out as not being descendants of Aaron at all.
Going back to Genesis 4 and 5 you can see a pattern: the sons of Cain were copying the sons of Seth, the former trying to make themselves appear as if they were the latter. For Cain was the father of Enoch, who was the father of Irad, who was the father of Mehujael, who in turn was the father of Lamech. We are told in Gen. 5 that Enoch (the seventh from Adam) was the father of Methuselah, who was the father of Lamech, who in turn was the father of Noah. As I've shown previously, Lamech (son of Cain) was a contemporary of Noah and was alive at the time of the Sumerian flood; whereas Lamech (son of Seth and Adam) died five years before the flood happened.
Another important point is: when Cain's line is detailed in Genesis 4, nowhere is Adam mentioned. This has to be attributed to the fact that Adam did not father Cain. It was the serpent (back in the garden) who sired Cain.
In conclusion, the sons of Cain injected themselves into Israelite society by way of the Nethinims--and later by way of the Edomite converts to Judaism in the 2nd century BC. By the time the Son of God arrived on the scene the sons of Cain had thoroughly infiltrated the Judean nation.
Jesus Christ was aware of this when he began his ministry in 27 AD. In John 8:33 the Jews "answered him, We be Abraham's seed, and were never in bondage to any man: how sayest thou, Ye shall be made free?" Here they are lying, since the Israelites (who were part of the Exodus under Moses) were enslaved in Egypt. These Jews--by their own words--prove that they "are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it."