William Shakespeare in this sonnet seems a bit concerned about the fact that his style of writing isn’t up-to-date with the new style of writing. Yet he seems to have accepted the fact that it can’t be changed, as it reflects him and his true feelings.
All he can write about is his love.
This song is a very famous song from the play Cymbeline. It simply means that you need not really fear death. Death is inevitable. Each one of us, be it royalty or the common class, everyone eventually will “come to dust”. All that we do and all that we become will lose its existence one day. And we need not fear it.