Pleading God‘s Promises in Prayer - Daniel

In response to God's promise that he would end his people's exile in Babylon after 70 years, Daniel senses the time is near and earnestly seeks God's face in confession and prayer for God's mercy in fulfilling that promise.  Which raises the question, why pray if God, who is sovereign has already promised.  Here in Daniel 9:1-19, we learn from Daniel about pleading God's promises in prayer.