I think the question arises from a twisted place.
FIRST there was slavery – humans are a sorry lot.
SECOND there was a rationalization that, since slaves could be held in Bible times, it’s OK now.
THIRD was the layered rationalization that Christianizing them helped them escape perdition.
But the question goes to ‘relationship with GOD.’ That has its own definition, one that shifts every so often. In 1619 when the first slave ship landed in Virginia, African people were considered pre-demeaned, hence of no account, hence it was no sin to own their bodies. The people who did that felt completely at peace with GOD, who sent his Son to die for them. Looking into the fine print is something every single generation does, to its own benefit, and wherever no benefit is found we wash that page clean and forget it.
Since GOD is viewed with changing eyes, nobody today who is Christian can give him-or-herself a pass for segregation, racism, and so on. That’s because we have a different view in the 21st Century. But in the 17th, those folks’ hearts got to feel at peace.
Only judge people by their own standards, not yours. Judge the standard, such as slavery, but try not to stand at God’s shoulder and whisper in His ear your judgement on people who did things you’d never do yourself.
Why? – how sure are you that, two or three hundred years from now, someone just like you will want to stand at God’s shoulder and whisper in His ear, about you?
Oh, and Another Thing 