The Roman church had many difficulties to deal with. One of them was the way in which Jews and Gentiles were to relate to one another in Christ. Paul exhorts them to not pass judgement on one another any longer. They are rather to consider how their actions might affect the walk of a fellow Christian. Such an exhortation is important to obey as pride so often hinders worship. The example of Christ and the work of his gospel bring people together in such a way that true worship takes place.
Building one another up is rooted in the gospel message—the hope of salvation we have in Christ Jesus. Paul exhorted the Thessalonian church to build one another up in the gospel, and through his letter to them he exhorts us to do the same.