What does Genesis 44:15 mean?

Joseph's latest plan has worked perfectly. His ten older brothers, who sold him into slavery twenty years ago (Genesis 37:24–28), are groveling at his feet (Genesis 44:14). With them is also the youngest of Jacob's sons, Benjamin. None of these eleven men recognize their estranged brother, who is now a powerful governor in Egypt (Genesis 41:44). Leaving with purchased grain, they were approached by Joseph's steward and accused of theft. Benjamin's sack was found to contain Joseph's own silver cup, much to their horror (Genesis 44:7–12). Now they have come to beg for mercy. They don't yet know the cup was placed there on Joseph's own orders (Genesis 44:1–6).

Judging by the full context of the story, this scheme is intended as a final test for Joseph's brothers. These men—other than Benjamin—had cruelly sold him into slavery simply to ease their own jealousy (Genesis 37:4). Now, they are faced again with the loss of a younger brother. His plan would show him if they had changed. Would they sacrifice Benjamin to save themselves? Would they feel bad about leaving him behind? Would they simply be thankful they were not also enslaved?

Now, as they lay in terror at his feet, Joseph speaks harshly. He again suggests he can practice "divination" (Genesis 44:4). This was the use of common objects to supernaturally tell the future or reveal information. Later in Israel's history, God would specifically forbid the practice (Deuteronomy 18:10). Of course, Joseph does no such thing, since he has direct knowledge from God (Genesis 37:5–9; 41:25–28). This seems to be Joseph continuing to "play the part" of an Egyptian vizier and further test his brothers.