Daniel 6:3 (ESV)

3 Then this Daniel became distinguished above all the other high officials and satraps, because an excellent spirit was in him. And the king planned to set him over the whole kingdom.

Darius recognizes that Daniel’s ability is greater than that of the other two officials. The Lord makes sure that Daniel can still do a lot, even in old age. Moreover he ensures that Daniel is also blessed with much wisdom and administrative energy. Darius intends to make good use of someone with such exceptional gifts. He plans to make Daniel the prime minister. It would mean that after Darius and Cyrus, Daniel would again become the third in the kingdom. He would become the most important and powerful man in this Empire after these kings.