“Welcome,” Paul starts chp 14 of Romans, “those who are weak in faith.” As NT Wright shows, we can’t be sure who the “weak” and the “strong” are — Paul thinks he is one of the strong — but the general idea seems clear.
Some people live as if there are no kosher food laws, while others think there are some restrictions. The issue could be eating, say, pork, while others see the issue to involve food offered to idols and where one can purchase such in the agora. However one defines it, Paul offers here a principle that Christians have had an enormous problem actually living:

How to deal with differences. Some tighten up things so the differences are minimal; others can live with considerable differences and it not bother them.
Notice Paul’s logic:
1. There are differences — whatever they might be and for whatever reason.
2. Neither is permitted to condemn or judge the other.
3. God welcomes each of the different parties.
4. Therefore, deal with the differences by tolerating them.
What kind of differences have been the cause of disruption in your local church?