What does it mean to be ordered by God to live long and prosperous lives?

The meaning of "I have been ordered by Heaven to live long and prosperous" is: (Since) (I) obey the destiny of Heaven and become (become) emperor; (I) should make the people live long and the country's destiny be prosperous forever.

In the 19th year of the Qin Dynasty (228 BC), Qin defeated Zhao and obtained He's Bi. After unifying the world, Ying Zheng was proclaimed the First Emperor and ordered Li Si to engrave the imperial seal in small seal script, with the characters "Ordered by Heaven? Live forever and prosper" engraved on the front. This jade seal is a token of the orthodox emperors of China.

Extended information:

The Jade Seal of the State was engraved by Li Si, the Prime Minister of the Qin Dynasty, on the order of the First Emperor, using He's jade. It is the certificate of the orthodox emperors of China.

It is four inches in diameter and has five dragons on it. The front is engraved with the eight seal characters "Ordered by Heaven, and you will live forever" written by Li Si as a token of "the imperial power is granted by heaven and is orthodox and legal".

After the Qin Dynasty, emperors of all dynasties regarded this seal as a talisman, treating it as a rare treasure and an important weapon of the country. If you get it, it symbolizes your "order from heaven", while if you lose it, it means you "have run out of energy". Anyone who ascends to a great position without this seal will be ridiculed as a "white emperor", showing lack of confidence and being despised by the world.