The underlying purpose woven through the OT of the Bible is effectively a plan to protect human dna from being desecrated.

Genesis discusses creation where God made humans in His image. Then the fall of man (corruption by sin) which is inherited by all offspring as an integrated part of our human nature. Shortly after the sons of God (fallen angels originally created by God in pre Biblical times) began taking for wives the daughters of man and the hybrid offspring known as the Nephilim resulted. In other ancient writings from Greek mythology to Indian mythology to the gods worshipped by the Canaanites and Babylon, these beings are generally know as demigods and according to the mythologies held non human powers and often enjoyed terrorizing and murdering and eating humans.

But why would this be? Well Genesis again provides the reason. God prophesied to Eve that out of her lineage would come a savior whom would crush the head of the snake (Satan). This was the first promise in the Bible that evil would be destroyed eventually and our human sinfulness would be excised as well at the end. Satan heard this prophesy as well and frankly being an angelic being and witness to the Creation events in the Bible was aware of genetics. Therefore the nephilim were the result of the first attack on the human genome by satanic aligned forces. The Flood was God's response. As the Bible records Noah was the only one left whom was just and perfect in his generations.

Sometime after the flood, God called Abraham out from his own people to be the father of what would become God's chosen people. Israel was the eventual outcome. The Hebrew people were commanded by God to not intermingle with other peoples. They were given strict rules that when followed would naturally prevent an attack such as the Nephilim from succeeding. They were also commanded to eliminate nearly all the people's of Canaan when they marched into the promised land in Joshua (the Bible identifies that many of the Canaanites had nephilim among them). Since it was promised to Abraham that the Savior would come from Abraham's lineage and since God secured that people's human genome in a way that the Hebrews held as the defining factor in their culture and heritage (chosen people who are set apart) the necessity or usefulness of a strategy of attacking humanities genome at large to create defiled hybrids (ie not in the Image of God) was diminished and the strategy was shifted more to trying to destroy Israel instead with other means.

After the Messiah, Jesus Christ, came to this world and fulfilled his mission to die as the required sacrifice payment for our sins. Jesus arose again from the grave demonstrating that He had accomplished all that he was purposed to do in bringing the promised salvation to sinful man. Satan's battle plan now shifted to persecute Christians and to decieve the Hebrews into rejecting Jesus, but that backfired as the Holy Spirit moved with the Gospel and many (Jews and Gentles) were given faith to believe and therefore saved. Next came infiltration to weaken the church from within with sin and wickedness. As all this happened over the ages man has been slowly increasing in knowledge until the inflection point of the last 200 years where our growth in knowledge has turned into an exponential upward curve.

Now man has come to know of genetics, and the possibilities of our changing our own code. This had opened the doorway for a reprisal of the pre-flood hybridization of the human genome. So that ultimately we may be no longer considered to be in God's Image. This is the reason that Matthew 24:22 records Jesus saying of the end times "And unless those days were shortened, no flesh would be saved; but for the elect’s sake those days will be shortened."

We are here now. And the tribulation is very near if not already begun. I cannot speak to where the line is as that will entirely be God's decision. I do believe the Mark of the Beast is something to do with genetics and/or cybernetic hybrid organisms.