What does Genesis 30:42 mean?
The previous verse restated Jacob's strategy of placing stripped sticks within the line of sight of the animals that were breeding to ensure that they gave birth to off-color animals that Jacob could claim as his own. However, he only did so for the strongest animals.God honored Jacob's device for indicating which animals he wanted to bear off-color offspring, causing those to be born in Jacob's favor and not in Laban's. Later, Jacob will clarify that he was given another dream from God, crediting the Lord with changing the nature of the flock (Genesis 31:7–12). Jacob doesn't think the sticks, themselves, are changing the sheep; rather, God is blessing Jacob by influencing the flock according to Jacob's wishes.
Now we see that Jacob removes his sticks from sight when the weak or feeble animals are mating. In this way, he ensures that those animals give birth to solid white sheep and solid black goats. Over time, this selective breeding would result in Laban's sheep and goats becoming weaker, while Jacob's became stronger.