Some of Paul's writings are very inspiring to me as I read them. Other writings (for example Paul's comments on women) tend to shock me. Surely in modern society we don't take Paul's advice on how to treat slaves or women, so how do we know what of Paul's writings contain useful knowledge for us as Christians and which can be taken merely as Paul's comments/opinions on the culture he found himself in while writing?
I know - it's not easy. It took me years before I even wanted to read the OT because of all the mass killings and ethnic cleansing.
We have to accept that Paul was writing from within a particular culture and that in any writing, whether by Paul or anyone else, there is tension between history and theology. It is also good to recognize that this tension between culture/history and theology is the dynamic creativity which creates doctrine and dogma. But when that theology gets expressed, as in the many texts of the Early Fathers, such tension is, 'on one hand ineffable and mystical, on the other manifest and more knowable' (Dionysios Epistle iX PG3). There is always a struggle to achieve anything like a balance.
All of which indicates that unless you read the Bible within your prayer life you will inevitable struggle to maintain that balance.
I could quite easily tell you to disregard what Paul says about slaves but would that assist you in any way? Probably not as such is only my personal opinion. As Bishop Kallistos Ware acknowledges, the Bible is a personal letter from God to you - what you do with it is largely up to you - but only if you treat the text with humility and reverence and not as something about which you wantb to make a political statement.
There is a story (I forget where I read this story) about two coloured men working in a factory some years ago who decided that they were not going to walk the extra 100 meters to drink at their designated drinking tap - they drank at the white's only tap. They were somewhat surprised that nothing happened - no one said anything yet any number of other workers had seen them. Shortly before they finished work a older white worker came up to them and informed them that if they drank out the white's only tap again he, the older worker, would get the sack. As he was only two years away from retiring with the company pension getting the sack would mean he would forego all of that pension. Now, what do you think the two coloured workers decided to do? If you were one of the coloured workers what would you have done?