"When Jacob saw that there was grain in Egypt, Jacob said to his sons, 'Why do you look at one another?' And he said, 'Indeed I have heard that there is grain in Egypt; go down to that place and buy for us there, that we may live and not die.' So Joseph's ten brothers went down to buy grain in Egypt. But Jacob did not send Joseph's brother Benjamin with his brothers, for he said, 'Lest some calamity befall him.' And the sons of Israel went to buy grain among those who journeyed, for the famine was in the land of Canaan" (Gen. 42:1-5).
Perhaps a year or so into the famine, the food supply of Jacob and his sons is running low. All of the brothers except Benjamin make the trip. Many other people are also heading to Egypt for the same reason.
"Now Joseph was governor over the land; and it was he who sold to all the people of the land. And Joseph's brothers came and bowed down before him with their faces to the earth. Joseph saw his brothers and recognized them, but he acted as a stranger to them and spoke roughly to them" (Gen. 42:6,7). It would have been exciting to witness the brothers speak with Joseph and bow down to him! They were, without even knowing it, fulfilling his childhood dream! It is incredible how much of a role dreams have played in Joseph's life. They do not recognize him after twenty years and in this great position of authority, but he easily identifies them. Certainly his appearance and attire had changed much more radically then theirs. Joseph's heart, no doubt, was stirred by the visit, but he pretends not to know them and accuses them of being spies. This enables him to have more dialogue with them and to learn about his father and younger brother. He then puts a plan in place so that he might be able to see Benjamin again.
Joseph spoke to them - "'In this manner you shall be tested: By the life of Pharaoh, you shall not leave this place unless your youngest brother comes here. Send one of you, and let him bring your brother; and you shall be kept in prison, that your words may be tested to see whether there is any truth in you; or else, by the life of Pharaoh, surely you are spies!' So he put them all together in prison three days" (Gen. 42:15-17). Initially, Joseph plans to keep nine of them in prison and allow only one to go home to bring back Benjamin. But, he later reverses this and allows nine to go home--perhaps out of compassion toward them or perhaps simply because he fears God (which he affirmed to them in 42:18).
"Then they said to one another, 'We are truly guilty concerning our brother, for we saw the anguish of his soul when he pleaded with us, and we would not hear; therefore this distress has come upon us.' And Reuben answered them, saying, 'Did I not speak to you, saying, "Do not sin against the boy"; and you would not listen? Therefore behold, his blood is now required of us.' But they did not know that Joseph understood them, for he spoke to them through an interpreter. And he turned himself away from them and wept. Then he returned to them again, and talked with them. And he took Simeon from them and bound him before their eyes" (Gen. 42:21-24).
Over twenty years have passed, but the first thing the brothers think of when they encounter this difficulty is that they are suffering because of their mistreatment of Joseph! It is likely they have reflected upon their wicked behavior toward their brother regularly. They regret it and still have strong feelings of guilt two decades later! Joseph is so moved by their words (which he understands, of course) and has to leave in order to weep privately and not expose his identity at this point. I don't think it was an accident that Simeon was bound. He was the second oldest behind Reuben, who had made an attempt to deliver Joseph initially.