"No Amendment shall be made to the Constitution which will authorize or give to Congress the power to abolish or interfere, within any state, with the domestic institutions thereof, including that of persons held to labor or service by the laws of said State."
To ease the fear of the Southern slaver owners that Lincoln would not interfere with their slaves, as he was not legally able to do in the first place.
What Lincoln ran on and intended to enforce was stopping any further expansion of slavery.
But you know this and these attempts to attack Lincoln for his 'racism'and his attempts to keep the Union together by ensuring the South that their constitutional rights would be protected under his administration, are simply attempts to muddy the water.