One very obvious point is that the Browning suggests spoken comments to a disinterested listener, while the Marvell is more like a letter to a girl he's trying to seduce: it doesn't use the conversational tricks which are common in the Browning. Clearly I don't want to write your whole essay for you and if you want more help from me, you would be wise to ask a more specific question, or say what in particular puzzles you.
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