Romans 14 - Family is family
People who trust and follow Jesus fall out about all kinds of stuff but they shouldn't. Ever.
Paul is talking in this chapter about Christians falling out over 'disputable matters' (v1). He's talking about silly arguments between people who trust and follow Jesus about what foods are ok to eat or whether or not one day is more special than the others. These are not matters of right and wrong. It's the motive that counts. Christians are allowed to eat whatever food they want to because Jesus declared all foods 'clean' (Mark 7:18-19), so Christians are free to avoid certain foods or eat them all, so long as they do all of it for Jesus, that's fine. Likewise, Christians are to keep the sabbath command by resting one day a week (Exodus 20:8-11) but it's primarily about having a sabbath heart that is at rest with Jesus every day of our lives (Hebrews 4:10).
Paul clearly has an opinion about these 'disputable matters'. He knows all foods are ok to eat and he knows that one day is not more important than the others but more importantly, he knows that Jesus makes his followers family. Jesus' family should not argue, fall out or separate over anything. Some Christians I know have left churches because they disagree about who gets to lead, some have left because they find certain people difficult to get on with, some have left because they think the guitars are too loud and still others have left because they think the guitars aren't loud enough! These are all rubbish reasons to leave a local church. Christians that leave over these issues are giving up on part of their family.
Paul says servants of Jesus should be united because they have the same master (v4). He says those who live for Jesus should be united because Jesus died to give them life in him (v7-9). He urges Christians everywhere to work hard to be united because Jesus has already united them (v19). How dare any Christian reject other Christians when God accepts all of them (v3)?! If we're trusting and following Jesus then he has made us family. And if we're going to be hanging out together in heaven with Jesus forever, then we might as well start practicing now!