Dan 6:1-3 It pleased Darius to set over the kingdom one hundred and twenty satraps, to be over the whole kingdom; and over these, three governors, of whom Daniel was one, that the satraps might give account to them, so that the king would suffer no loss. Then this Daniel distinguished himself above the governors and satraps, because an excellent spirit was in him; and the king gave thought to setting him over the whole realm.
From the prophecies of Jeremiah, Daniel was given the vision that Israel would be in desolation for seventy years. The Jews were instructed to serve the conquerors in peace. So Daniel obeyed Yahweh and served the conquerors faithfully. This excellent spirit set Daniel to excel over all the other governors and satraps, prompting King Darius to promote him above all the others.
Dan 6:4 So the governors and satraps sought to find some charge against Daniel concerning the kingdom; but they could find no charge or fault, because he was faithful; nor was there any error or fault found in him.
Out of jealousy, the governors and satraps planned to destroy Daniel even though they knew that he was faultless.
Dan 6:5, 7 Then these men said, "We shall not find any charge against this Daniel unless we find it against him concerning the law of his God."... All the governors of the kingdom, the administrators and satraps, the counselors and advisors, have consulted together to establish a royal statute and to make a firm decree, that whoever petitions any god or man for thirty days, except you, O king, shall be cast into the den of lions.
The wicked plan of Daniel's enemies was to get the king to forbid everyone from petitioning any god or man for 30 days, knowing that Daniel would not conform and would still continue to pray to Yahweh.
Dan 6:11, 13 Then these men assembled and found Daniel praying and making supplication before his God... So they answered and said before the king, "That Daniel, who is one of the captives from Judah, does not show due regard for you, O king, or for the decree that you have signed, but makes his petition three times a day."
All evidences of Daniel's disregarding the king's decree (praying 3 times a day to Yahweh) were presented before King Darius.
Dan 6:14-15 And the king, when he heard these words, was greatly displeased with himself, and set his heart on Daniel to deliver him; and he labored till the going down of the sun to deliver him. Then these men approached the king, and said to the king, "Know, O king, that it is the law of the Medes and Persians that no decree or statute which the king establishes may be changed."
King Darius was angry with himself for being deceived to sign such a decree, which would definitely send his faithful, loyal and godly Daniel to his death. He was trying his best to save Daniel from certain death in the lion's den.
Even the great King Darius, who wielded supreme power could not abolish his decree to save Daniel, unless he was prepared to break the law of the land.
How much more for our Lord God Almighty that though He is Sovereign, He will not go against His words, promises, covenants, etc. because He cannot and will not sin. As a just and righteous God, He is always faithful to His words and promises.
So brethren, always abide in His love and be blessed with His presence, guidance, peace, joy, wisdom, understanding, knowledge, and empowering of the Holy Spirit as promised by our Lord Jesus Christ.