What was the mark God put/set on Cain for his protection (Gen.4:15)?
It was not a “mark” “on” Cain; it was a “sign” “for” Cain. I happen to be a full-time Bible translator, have taught both Hebrew and Greek and not long ago corrected the manuscript for the Ukrainian Bible Society, so everything I’m telling you I could prove if need be with all kinds of documentation. Cain feared that at some time in the future, a brother would be born to Adam and Eve who would hunt him down and punish him with death for murdering Abel. God promised that that wouldn’t happen. Cain, not surprisingly, had trouble believing that God would be that gracious. To convince Cain that God meant it and could do it, God gave Cain a sign. We don’t know what it was. Maybe water flew uphill or the sun turned blue or a force-field shimmered around him. But it was no sort of mark on Cain’s body, and most certainly was not a change in his skin color.
Nobody knows what the mark was, but I believe it had something to do with the mark of the beast. I also believe that Cain took his wife from the human like people that live before and during the time that God created Adam and Eve. If you look in the linage of Cain you will find that Lamech (Cain’s great grandson) killed Cain and was to be punished 70 and 7 fold times. Also if you look you will see that people was experts in iron and brass and this was only about 6 or 7 generations from Adam. Now someone tell me that there was not some form of human like creatures here at the time of the creation of Adam and Eve. Only thing is: they didn’t have a soul at that time. Only after God breathe into Adam’s nostrils did man become a living soul.