Question

what is poets message in not marble nor the gilded monuments

Answer 1

The message conveyed in this poem is that people think that they will be remembered by all if they build monuments of their own. But that's not true. Monuments fade over time. 

The thing which actually is worth remembering, according to the poem, is literature. You can destroy monuments, but you cannot destroy someone's writings. Writings pass down from generations to generations. Literature is far more valuable than these gold or marble statues. This is because unlike monuments, literature never fades away.

Answer 2

The poets msg in this poem is time is more powerful than anything else but the memory of his friend is more powerful than time