Christians are called to be kind to one another, tender-hearted, and forgiving one another. But this cannot be done apart from the gospel. Love for the gospel is the root cause and enabler for Christians obey this command.
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.