The first occurrence.
The sons of God saw that the daughters of men were fair; and they took wives from them of all which they chose. Gen 6:2
The primitive root.
Strong’s H977 בחר bachar, a primitive root meaning, “to choose.” The 3-letter root is bet + chet + resh.
bet ב = the house, thus house, household, family, in, within
chet ח = the wall, thus outside, divide, half
resh ר = the head of man, thus head, first, top, beginning, man
The story: The cognate words will help us find the story, two of which are slaughter, and knife. So beyond the house (bet) is the wall (chet), a metaphor for work that is done outside. Slaughtering an animal was a task performed outside the house. Slaughtering (bet + chet) that which is chiefest or choicest (resh) indicates the sacrifice, the firstfruits in its concrete meaning; but an examination to determine the choicest, thus to choose, in its verbal meaning.