Lincoln is a complex man, and it's sometimes difficult to understand him because he left no personal diary and often didn't express his personal feelings. I should also note that many forget that Lincoln was human, and thus he could change and improve. It always annoys me when people use his 1854 quotes to explain why he was a bad President. That said, it's an undeniable fact that Lincoln was not in favor of racial equality as we understand it, but neither was he a callous White Supremacist as some people have maliciously claimed. The answer is somewhere in the middle.

Lincoln was born in Kentucky, though his earlier memories were in Indiana. He then moved to Illinois. Indiana and Illinois were part of the "Lower North" states settled by Southern immigrants. Many of these immigrants, including the Lincolns, came from states and territories where a chaotic settlement had made land titles insecure and often produced lawsuits that only the wealthy could win. Since wealth was associated with slaveholding, many of these settlers resented slaveholders but still carried with them deep prejudices against African Americans. Lincoln's family was certainly not rabidly racist, but neither was it some kind of egalitarian luminaries. Furthermore, Lincoln never interacted with Black people that much, the first time he actually saw African slaves being in a trip down the Mississippi. He only had true contact with Blacks after becoming President.

An upbringing like this certainly was not enough to form a complete egalitarian. Radical Republicanism flourished in New England and the areas of the North settled by their immigrants, and the most well-known Radicals like Sumner or Stephens were raised in New England. Lincoln was raised in states known for their Democratic sympathies and racism. Despite this, Lincoln declared that he had always been naturally anti-slavery, to the point that he did not even remember a time when he didn't feel that way. As he grew from boy to man, and despite not being in contact with slavery except from some trips to the plantations of his intimate friend Joshua Speed, Lincoln developed a very strong anti-slavery opinion.

What distinguishes Lincoln from the Democrats or the most conservative Republicans is the fact that Lincoln always considered slavery to be a moral wrong. Some Republicans focused only on how slavery was not sound economically, denounced the Slave Power, or believed that abolishing slavery had to be done for the benefit of White men. Lincoln never wavered in his opinion that slavery was a "monstrous injustice" and he always recognized the humanity of African Americans, a position that was radical in an era where they were often reduced to inhuman chattel. This you can see in his debates with Douglas, who always denied the basic humanity of African Americans and accused Lincoln of being a Black Republican who thought of Blacks as his brothers. In these debates, even as Douglas loudly denied that Blacks could have any rights at all, Lincoln said that Blacks were humans, entitled to the basic rights of life, liberty and the pursuit of happiness.

This, again, does not mean that Lincoln was a complete egalitarian. At the core of Lincoln's position regarding the slavery issue is the simple fact that he both hated slavery and loved the Union. And Southerners had made it quite clear that any attempt to interfere with slavery would lead to disunion, and the very American Constitution, a document Lincoln and most Americans cherished as the foundation of their happiness and safety, protected slavery. It was quite a dilemma - he could not advocate for the end of slavery without coming across as a disunionist. Furthermore, even if Lincoln was willing to recognize the humanity of Blacks, there were many Northerners who felt apathy at best and hate at worst towards them and were completely horrified at the prospect of disunion. This explains a wave of violence against abolitionists during the 1830's - Northerners were not rioting because they loved slavery, they were rioting because they loved the Union and hated those who, in their eyes, advocated for its dissolution.

There was also the fact that Lincoln simply didn't know what was to be made of African Americans once freed. Here Lincoln's own prejudices become apparent as he was not ready to afford them true equality, yet he recognized that just liberating them but giving them no rights and no meaningful liberty would not be an improvement either. Lincoln settled in colonization as a "solution". Colonization entailed sending African Americans out of the United States to Liberia or Latin America, as a way to eliminate their presence and thus racial discord. The idea so obsessed Lincoln that he even tried to put it into operation during the Civil War. It did not come from a place of hate, but from a since belief that there was no way African Americans and Whites could live together in harmony and that emigrating to other lands was the only way for Blacks of achieving true happiness. Altogether, colonization was an attempt by Lincoln to evade the problems of slave emancipation.

This same evasion can be seen in his debates with Douglas, who pressed Lincoln to answer how the "ultimate extinction" of slavery would actually take place. If immediate abolition meant civil war and racial discord, something no one in the North except the radical fringe wanted, then it wasn't really an option. But what could be done then? Lincoln, like most Republicans, subscribed to the idea that slavery was inherently bad for the economy and well-being of a society, and if left without room to expand, it would simply die out. That's why Republicans pushed for the goal of Free soil in the territories, a goal that seems rather useless as an anti-slavery measure yet it was the only meaningful action they could take for the moment. This is what Lincoln meant with "ultimate extinction", yet when that would happen exactly? In a hundred years or so, Lincoln answered.

Take into account that Lincoln was running for an Illinois Senate seat. Illinois, a state that had never elected a Whig as Governor or Senator, and the Republicans were largely made of former Whigs, Lincoln included. Illinois, a state with a large population of very racist "Butternuts", men who during the war were known for their violent opposition to slave emancipation. Was Lincoln merely an opportunist who would say anything to win the seat? It's unlikely, for he was expressing real principles, and the simple fact that both him and Douglas were actually not that different in actual policies made the debates all about the meaning of slavery in the United States and what was to be done about it. Did Lincoln have to moderate his message to appeal to Illinois voters? Most assuredly. Douglas himself said that Lincoln became more moderate the farther South he went. Altogether, Lincoln's statements against racial equality were part genuine opinion, part political messaging.

So, Lincoln occupied a middle between the conservative Republicans and the Radicals. He genuinely hated slavery, but was conflicted about what to do to actually end it. He recognized the humanity of African Americans and afforded them respect and kindness (Frederick Douglass would declare that Lincoln was devoid of prejudice against Blacks for example), yet he was not ready yet to afford them immediate freedom with all its implications. He was not a racial egalitarian, but neither was he a callous White Supremacist. It's, like people tend to be, a grey situation full of nuance.

As the Civil War developed, Lincoln started to change. It's dangerous to attribute this to some kind of predetermined growth, and Lincoln himself admitted that he was the victim of events outside his control. Nonetheless, Lincoln's opinions changed, that much is certain. Much is said about how he insisted on the war being solely for Union at its outset, or how the Emancipation Proclamation only freed those in rebel areas. Yet Lincoln had to do this because he had to take into account a host of complex political factors to maintain the loyalty of the Border States and many Democrats who would fight for Union but not for Liberty. What is the use of freeing all slaves from day one if that results in a rebel victory? And for those who say that Lincoln did nothing against slavery, he continuously took anti-slavery measures that would have been hailed as gigantic triumphs in the ante-bellum and seemed useless only due to the rapid development of the war: free soil for all territories, anti-slavery treaty with Britain, a push for slave emancipation in the Border States (where he had no constitutional power to interfere with slavery), etc.

Lincoln's moral concern for Blacks was evidenced time and time again. Some say he did not care for Blacks but only for winning the war, yet after the Emancipation Proclamation he always insisted on the twin goals of Union and Liberty despite extreme pressure to settle for Union. He likewise directed commanders to treat the contrabands fairly and refused to continue prisoner exchanges unless the Confederates treated Black soldiers equally. Towards the end of the war, as he had to contemplate a nation without slavery where Blacks and Whites would have to live together, Lincoln took his most daring steps in favor of equality. He signed the bill creating the Freedmen's Bureau, which had the power to distribute confiscated lands, and pushed for limited Black suffrage in the South. By that time, he and the great mass of Republicans had come to the conclusion that Blacks deserved civil equality, though the prospect of political equality was still far away.

Lincoln was not a racial egalitarian as we would understand today. He certainly had prejudices proper of a 19th century man, and was not ready to afford full meaningful equality to Blacks. But he still expressed sympathy for Blacks and was willing to give them legal equality.

TL;DR: Lincoln was fairly progressive by the standards of his day, though some of his statements appear shocking to modern sensibilities (particularly prior to 1862, before he issued the Emancipation Proclamation). His views definitely changed over time, though he was significantly less racist than many of his contemporaries in 1858.

In 1858, when the Lincoln-Douglas debates took place, Lincoln was advocating for the end of slavery. At the time, this position was itself fairly radical, and advocating for full equality between whites and blacks would have been an even more radical position. Remember that in 1858, Lincoln is running for a U.S. Senate seat and speaking to an electorate that is entirely white.

Historians debate whether Lincoln truly believed some of the things he said regarding equality during the Lincoln-Douglas debates, but it seems safe to say that his views did evolve significantly by the end of his life. I've seen various passages from the Lincoln-Douglas debates pop up on social media over the last few weeks, and while many of them seem striking out of context, it is worth reviewing his full remarks to get a sense of where he stood in 1858 (let's assume for now that his comments reveal his true feelings and not a political calculation, as some argue).

The quote I've seen pulled out the most is from the the First Lincoln-Douglas debate (August 21, 1858):

"I have no purpose to introduce political and social equality between the white and the black races. There is a physical difference between the two, which in my judgment will probably forever forbid their living together upon the footing of perfect equality, and inasmuch as it becomes a necessity that there must be a difference, I , as well as Judge Douglas, am in favor of the race to which I belong, having the superior position."

HOWEVER, what almost always gets left out is the very next sentence. Lincoln continues: "I have never said anything to the contrary, but I hold that notwithstanding all this, 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."

This is a relatively progressive view for a U.S. Senate candidate in 1858. Lincoln is trying to craft a very delicate argument here. He's trying to advocate for the end of slavery while also reassuring his white audience that the end of slavery is not a threat to their social standing in the world. Lincoln knows that Douglas is trying to convince the voters that Lincoln is a radical abolitionist, and Lincoln knows that a radical is not likely to win a U.S. Senate seat in Illinois in 1858. Throughout the debates, Lincoln tries to argue that ending slavery is not a radical position and that finding some way to end the institution, however gradually, is the only way to ensure the long-term viability of the American nation. Of course, Lincoln doesn't win that race, so his arguments clearly didn't carry the day.

Compare this to Lincoln's statements in his Last Public Address nearly 7 years later (April 11, 1865). In this speech, Lincoln openly calls for blacks to be given the vote. In advocating for the State of Louisiana to restore their "proper practical relation with the Union" (Lincoln believe that secession was illegal, and that the Confederate states were never not part of the U.S., ans so avoided using the word "readmitted") he says:

"It is unsatisfactory to some that the elective franchise is not given to the colored man. I would myself prefer that it were now conferred on the very intelligent, and those who serve our cause as soldiers."

Though the idea that only the "very intelligent" should be allowed to vote may be offensive to modern sensibilities, this idea was so objectionable to some at the time, that Lincoln was assassinated three days after he made this statement. Is is clear that his views on equality changed between 1858 and 1865.

First Lincoln-Douglas Debate: https://www.nps.gov/liho/learn/historyculture/debate1.htm

Lincoln's Last Public Address: http://www.abrahamlincolnonline.org/lincoln/speeches/last.htm