I speak on due consideration ...

I speak on due consideration because Britain, France, and Mexico, have abolished slavery, and all other European states are preparing to abolish it as speedily as they can.
 William H. Seward

Quotes from the same author

It is the maintenance of slavery by law in a state, not parallels of latitude, that makes its a southern state; and the absence of this, that makes it a northern state.
 William H. Seward
The color of the prisoner's skin, and the form of his features, are not impressed upon the spiritual immortal mind which works beneath. In spite of human pride, he is still your brother, and mine, in form and color accepted and approved by his Father, and yours, and mine, and bears equally with us the proudest inheritance of our race - the image of our Maker. Hold him then to be a Man.
 William H. Seward
I mean to say that Congress can hereafter decide whether any states, slave or free, can be framed out of Texas. If they should never be framed out of Texas, they never could be admitted.
 William H. Seward
There is not only no free state which would now establish it, but there is no slave state, which, if it had had the free alternative as we now have, would have founded slavery.
 William H. Seward
The proposition of an established classification of states as slave states and free states, as insisted on by some, and into northern and southern, as maintained by others, seems to me purely imaginary, and of course the supposed equilibrium of those classes a mere conceit.
 William H. Seward