"Death, be not proud"

"Death, be not proud," by John Donne is a very interesting poem. It talks about death in a way that is not often heard. It speaks on how death is really not all that powerful. It is not something to fear, it is something to embrace, though it has little power. Death holds no power, the poem says "Thou art slave to Fate, Chance, kings, and desperate men." This means that death's power is overshadowed by the actions of the great like kings, and the lowly such as the desperate. This all makes sense as one reads the poem. The one thing that is confusing, however; is when the poet mentions sleep. I didn't really understand where he was going with that, and am puzzled as to what he means. I think he is saying that death and sleep are essentially the same thing, which I don't quite get, and because of that one ought want death, for it would bring the same  good tidings that sleep does. Overall, I enjoyed the message of the poem, but likely because of the dated diction, part of his message was lost to me.