And God sent me before you to preserve for you a remnant on earth, and to keep alive for you many survivors. So it was not you who sent me here, but God. He has made me a father to Pharaoh, and lord of all his house and ruler over all the land of Egypt.
I believe that the tears of joy that Joseph wept at his "unveiling" to his brothers came from two sources. The first was the joy in seeing the change that was occurring as circumstances and age began to humble his brothers. This was for him a moving moment, considering that he had endured slave status, had been falsely imprisoned and forgotten there, and had been exalted not only to Pharaoh's court, but to chief administrator of the surplus wealth of Egypt. His life was an emotional rollercoaster! This was just another part of the ride.
But the second source of the tears of joy is pure spiritual insight. Joseph has managed to slowly stitch together how the providence of God has cared for him and his family. This is overwhelming. God used the most horrendous things that happened to an innocent young man for His glory and the salvation of many souls. Think about all the bad actions God managed to weave around in order to sovereignly provide for His covenant with Israel. Joseph was favored unfairly by his dad, creating family strife. God gives the young man revelatory dreams to help him cope and serve notice to the family of a future for him. Joseph has no control over his brothers' disdain. He is sold into slavery, and God sends him to the captain of the Pharaoh of Egypt where he excels. He is falsely accused of sexual assault, God makes sure that because of Potiphar's status, Joseph ends up in a royal prison where he eventually interprets the dreams of two members of Pharaoh's court. Then God uses the dreams of Pharaoh to pull Joseph from the pit to the position of prime minister over all of ancient Egypt in one day. God uses the famine to bring Joseph's family back to him, where he serves in power, and the dreams of a boy are brought to fruition for the glory of the God of the covenant.
God's providence is beautiful. It brings joy. It moves us with emotion. It must, for when we see the wisdom of His ways, we see His love, His holiness, His justice, and His power. All of that is condensed down to this intense moment that Joseph has with His brothers. All that they had done that was bad, had somehow been turned by God for His purposes. He cannot change. He will not be undone by human will, no matter how bad we sin. And Joseph knew this. It was literally the story of His life.