What were the differences between the views of the northerners and the southerners on slavery?

Southern leaders were highly motivated to defend slavery because it was the mainstay of the vastly profitable cotton industry. As the slavery debate heated-up in the 1850's, they put pressure on church ministers to preach that slavery was a perfect God-given arrangement of master and man. This began to influence people who should have known better. Robert E. Lee declared that slavery was an evil which the Almighty would bring to an end when He saw fit. Lee cannot seriously have believed this.

The North was not united against slavery by any means, but the Abolitionists were a powerful lobby, and they also encouraged preachers to denounce slavery as a sin against human beings created in the image of the Lord.

It should be noted that the men in the ranks of the two armies in the Civil War mostly didn't care about slavery, one way or the other.