The mixing of DNA from both parents at conception is what produces the pattern that determines physical and mental tendencies. These make that child differ from all others. This occurs even before the “parts” are formed, just as the psalm continues, “as regards the days when they were formed and there was
not yet one among them.” Those ‘parts down in writing’ are not just a “piece of tissue.” The potential personality traits of each embryo are there for the Creator to see, as if in his “book.”
With this background, we can see how God could say to Jeremiah: “Before I formed you in the womb I knew you for my own;
before you were born I consecrated you.” (
Jer. 1:5,
The New English Bible) Notice that God viewed Jeremiah as a separate person while still in the unborn state. He could “know” him and judge him worthy for God’s special work because an immeasurable number of Jeremiah’s potential traits had been determined within minutes of his conception!
From Jehovah’s conversation with young Jeremiah, it is clear that he was one of the few men for whose birth Jehovah assumed responsibility. And why did he take specific interest in Jeremiah from his conception onward? Because Jehovah had a special commission in mind for him. Thus, he could say: “Before you proceeded to come forth from the womb I sanctified you.” (
Jeremiah 1:5)
As far as hating Esau, God didn't say that he hated Esau while Esau was in his mother's womb. The only thing God said while Esau was in his mothers womb is that the older(Esau) would serve the younger. When the scriptures say that God hated Esau it was because Esau had no respect for what God loved, meaning spiritual things, after all Esau sold his firstborn rights to Jacob for a bowl of stew.