It's " Sloth, you silent murderer,
No more my mind imprison'd keep"
It means that when you slothful, your mind isn't working, isn't free- the person wants to break away and recover their powers of imagination, etc.
Poems do follow grammar, but not all the time- they are far more lkely to break away from conventional grammar than most prose. This, however, is quite old English and probably was easier to follow in the time it was written. The word order is different from today, but you will still find it used for rhetorical effect.
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