What does Genesis 30:40 mean?
The previous verses described Jacob's strategy for getting the black goats to produce striped, speckled, and spotted offspring. This verse describes his method for getting the white sheep to produce black lambs. This is a notoriously difficult verse to translate, and to interpret. It's possible that Jacob caused the white sheep to mate while facing the black and striped animals in the flock, causing them to produce black offspring.Once more, this isn't intended to show that either Jacob or the Bible believed this to be a scientific method for breeding off-color animals. Jacob understood from the Lord that the flock was going to yield off-color animals (Genesis 31:7–12). The Lord honored Jacob's method for identifying which of those animals he wanted to produce off-color offspring and caused it to happen. As the following verses will reveal, Jacob did not want all of the animals to be striped, speckled, spotted, or off-color.
As the off-color animals were born, Jacob separated them from the rest of the flock. In short, he separated his burgeoning flock from Laban's, allowing him to keep track of just how quickly his own wealth was growing.