What does Genesis 44:10 mean?
Joseph's brothers have been defending themselves from what seemed like wild accusations. Joseph's steward has accused them of stealing his lord's personal silver cup (Genesis 44:4–8). They insist that they would never do such a thing, rashly offering that if any of them is found with the cup, that man will die. More, all the rest will become servants of the Egyptian ruler (Genesis 44:9). They have no idea that the Egyptian governor is their own estranged brother (Genesis 42:7–8).The steward knows the silver cup is in Benjamin's sack, because he placed it there on Joseph's own order (Genesis 44:1–3). Probably in accordance with Joseph's wishes, he pounces on their foolish offer, but changes the terms. Instead of killing the man found with the cup, that man shall stay behind as a slave of his master. The rest of them will be free to go.
Taken in full context, this seems to be yet another test by Joseph. He seems interested to know if the men will once again abandon a younger brother to meet their own selfish ends. That's exactly what they—other than Benjamin—had done some twenty years prior (Genesis 37:24–28).
