"Then these men went as a group and found Daniel praying and asking God for help. So they went to the king and spoke to him about his royal decree: 'Did you not publish a decree that during the next thirty days anyone who prays to any god or man except you, O king, would be thrown into the lions' den?' The king answered, 'The decree stands - in accordance with the laws of the Medes and Persians, which cannot be repealed.' Then they said to the king, 'Daniel, who is one of the exiles from Judah, pays no attention to you, O king, or to the decree you put in writing, He still prays three times a day.'" NIV translation
So, these politicians sprung their trap and caught Daniel praying to God as they knew they would. They report this to the king in a detached kind of way as if they were only looking out for the interests of the king. They remind the king that Daniel is not a Babylonian and that he is breaking the law. This is a reminder to us that, like David, we must listen and follow our heavenly King even if that goes against the edict of an earthly king. Daniel knew that there would be a penalty in his choice but he also knew that God was ultimately in charge.
"When the king heard this, he was greatly distressed; he was determined to rescue Daniel and made every effort until sundown to save him. Then the men went as a group to the king and said to him, 'Remember, O king, that according to the law of the Medes and the Persians no decree or edict that the king issues can be changed.'" NIV translation
The king did all that he could to save Daniel but even he could not change the law. The king was at risk if he did not carry out the punishment that was prescribed by his own decree.
This is a picture of the hopelessness of man under the Law of Moses. Like the law of the Medes and the Persians, God's Law could not be changed even by God.
"So the king gave the order, and they brought Daniel and threw him into the lions' den. The king said to Daniel, 'May your God, whom you serve continually, rescue you!' A stone was brought and placed over the mouth of the den, and the king sealed it with his own signet ring and with the rings of his nobles, so that Daniel's situation might not be changed." NIV translation
The king obeyed his own decree and had Daniel thrown into the cave with the lions and even "prayed for him". The entrance to the cave was sealed by a large stone and the seals of the king and the nobles. They did this so that nobody could let him out without their knowing about it. This is a picture of what would happen when Jesus was taken down from the cross. His tomb was also sealed with a stone and guards were even placed outside.