Why did Lincoln require ten percent for his plan of reconstruction?

So that a southern state could be readmitted into the Union once 10 percent of its voters swore an oath of allegiance to the Union. Voters could elect representatives to draft state constitutions and create state governments. All southerners except for high-ranking Confederate officers and government officials would be given a full pardon. Lincoln promised southerners that he would protect their private property, not their slaves. Most moderate Republicans in Congress supported the plan because they wanted to bring a quick end to the war.