For what purpose did Lincoln suggest these three standards: owning property, being able to read and write, or having served in the Union military?

Lincoln suggested these three standards for African Americans to vote.

Despite the fact that Lincoln was an abolitionist he did not think that African Americans were equal to white people. This way he tried to reduce their rights by passing standards for them to vote. An African American would have to own property, read or write or even served in the Union military. Lincoln even stated in a debate between him and Douglas on August 21, 1858 "I have no purpose to introduce political and social equality between the white and the black races ... there is no reason in the world why the negro is not entitled to all the natural rights enumerated in the Declaration of Independence, the right to life, liberty, and the pursuit of happiness".