Even noble men, God fearing men can be terribly wrong. We have the benefit of time to view his actions yet still he had a choice and he chose his State over freedom and liberty of his black brethren.
The Constitution protected the rights of the Southern States.
And what rights? The right to enslave fellow human beings against their will?
He made a terrible error yet was still a great man. There is a lot we can learn, like being a devout person of prayer.