Da 1:7 The chief official gave them new names: to Daniel, the name Belteshazzar; to Hananiah, Shadrach; to Mishael, Meshach; and to Azariah, Abednego.
What determines who we are? When someone asks "Who are you?" we give them our name. When they ask "What are you?" we give them our job. We also talk about ourselves in terms of where we live, where we are from, our family and friends.
Daniel and his friends had all this taken away from them. They lost their homes, their jobs, their family, friends, their country, their place of worship, even their names were changed. Yet they did not lose their sense of identity. They had something deeper. What was it?
God also changes names in scripture. To Abram he gave the name Abraham (father of many), to Simon, Jesus gave the name Peter (Rock). In both cases it came after a powerful encounter or revelation of God, and deepened their sense of identity. It shows that our true sense of identity comes not from without (the things we have) nor even purely from within... but from above. We will never really know who we are until we know God, and know who we are in him.