What does this mean?????????

im doing a project for us history n well what does this exerpt from an andrew jackson letter mean?Jackson wrote with reference to the role of Charlestonian Henry Laurens Pinckney in securing page of resolutions that led to the adoption by the House of the policy of tabling all petitions for the abolition of slavery, "they embrace the most important of those considerations of expediency on which the citizens of the non slaveholding states can give us the aid of their cooperation in checking what is manifestly dangerous to the peace and harmony of the country....the temperance and patriotism you have evinced in sustaining him are deserving of the highest commendation and cannot fail to secure you the approbation of a liberal and generous public."