How ruthless are the gentle--

How ruthless are the gentle--
How cruel are the kind--
God broke his contract to his Lamb
To qualify the Wind--
(F 1465)

This is one of probably dozens of Dickinson's poems that has confuses me. I really don't know what it is "supposed" to be about, and the last line doesn't seem to make much sense at all. That said, the first two lines are intriguing. It makes me think perhaps this is a commentary on society and what is "dignified" and "proper." It seems that so much of what was socially acceptable and the "refined" behavior of the upper class could be truly cruel and brutal. Lives, physically and emotionally and likely mentally, could be pulled apart with one wrong word or move.

Perhaps it could also be a commentary about institutions like slavery. The southern states defended slavery, often claiming the Africans taken as slaves were less intelligent, not human, and that it was for their own good. The "gentle" treatment is revealed in horrifying detail in books like Harriet Beecher Stowe's Uncle Tom's Cabin, and even the most well-meaning of those who keeps slaves only perpetuate a system of pain and separations, even death.

I wish I understood the last line.