This is a personal prayer, and yet it is more than that, because it introduces the prophecy that he is given. The prayer was obviously published with the prophecy at that time.
Why did Daniel pray if he knew this was certain to come to pass? Although he had read Jeremiah and knew that it was the will of God that the Jews should return, he was not complacent about this. His reaction to the prophecy is to pray. He fully believed the prophecy, but it did not stop him from praying to God for the very thing that prophecy had said should certainly come to pass. He understood that they did not deserve such goodness from the Lord, and that they had not yet humbled themselves before the Lord as they should. He understood God’s use of means: in this case prayer. Prayer is part of the appointed means for bringing about the will of God, and in the plan of God it is a necessary means. The certainty of the elect being saved and of our final victory over sin and darkness, does not diminish the urgency of prayer. Christ too prayed with intense earnestness in John 17 that the Father would keep those given to him from the evil. He prayed this even though he knew their names were written in the Lamb’s book of life from before the creation of the world. We thank God that we have been given this vital role, and we summon all our strength to carry it out. There are those who take a fatalistic view and argue that God will save his elect with or without our prayer and efforts. Such people will never be greatly used by God in his harvest.