Why does the poet think that the glories of our blood and state are shadows?

The Glories of Our Blood and State is a seventeenth-century poem written by James Shirley. This poem largely focuses on the themes of mortality, death, and the nature of glory and success.

The glories of our blood and stateAre shadows, not substantial things; There is no armour against Fate; Death lays his icy hand on kings:

In the first four lines of this poem, Shirley claims that the glories of our blood and state are unsubstantial, or simply a shadow of something that is mistakingly viewed as important. What is his initial evidence to this fact? Despite the great successes that are seen to be achieved by kings and noblemen, they are not any more immune to death than the common folk.
Death takes us all, no matter how much blood we spilled, how many victories we won, how much land we owned, or how much our state defeated another state in battle (note the period in which the author lived!).
Towards the end of this poem, he writes,

Only the actions of the justSmell sweet and blossom in their dust.

Although Shirley lived in a society in which monarchy, bloodlines, battle victories, and land ownership were deemed to be so pressing and important, he writes about how these things are meaningless and leave behind nothing beautiful in the world as the cycle of violence on Earth continues.
In those final two lines, he declares that only those who do genuine good in the world, rather than continue these deadly cycles, will have some level of glory in death.