Paul begins Romans 14 by speaking of the "weak in faith" and in 15:1 he urges "we who are strong" to "put up with the failings of the weak."
Arland Hultgren is probably right to conclude that Paul does not use "strong" and "weak" to define particular groups of people in Rome.
Instead, Paul is clarifying his thinking about food and festivals for Christians who do not know him, and who may have heard that he "went off" on Peter for withdrawing from table fellowship with gentiles (cf. Galatians 2:11-14) and that he voiced strong opposition to the Galatians observing "special days, and months, and seasons, and years" (Galatians 4:10). The advice Paul offers here is calmer and more considered in tone.
If we did not know the Galatians passages, it would be easy to read Romans 14 and think, "Food and festivals: so what?" In Romans, Paul offers the advice that people should welcome one another and not judge different convictions. Good advice, we think, but the issues he mentions seems so much smaller than the issues we struggle with: how to define ethical and moral sexual relationships, whether the wars we are fighting are just, what the arrival of new immigrants means for our communities, churches and nation.
Most of us would hardly notice it if someone labeled a few dishes "vegetarian" at the church potluck. Reading the Romans text in isolation might lead us to conclude it had little to say to churches that are struggling with church-dividing issues.
Yet Galatians makes it clear that, at least in one context, these apparently inconsequential issues threatened both the church and the gospel. Ten years or so before Paul wrote Romans, food and festivals were huge issues. A decade or so later, the apostle who was combative when writing to the Galatians can, in the context of his letter to Rome, exhort readers to welcome one another across different opinions and practices on the same issues.
Why the change? Paul does not imagine that anyone among the Christians in Rome is requiring certain Jewish practices related to food and other things, such as circumcision. By contrast, in Galatia, the teachers who followed Paul did seem to be requiring these things. It is probably also true that no one in Rome is attempting to substitute the observance of days or abstinence from eating meat for the saving work of Christ, while opinion and practice related to clean/unclean food and the correct observances of days had (at least in Paul's opinion) reached that level in Galatia.
So the question that Romans 14 answers seems to something like this: "When no one is claiming another Savior besides Jesus or leaning on a source of righteousness besides the righteousness of Christ, and yet the church disagrees, what do we do?" And the answer Paul gives is to welcome one another (14:1) and to put up with each other's failings (15:1). Actually, he tells the strong to behave this way toward the weak, but his words still resonate with both sides, for who on either side of any debate does not imagine themselves to be the strong and their opponents to be the people who just don't "get it" yet?
Paul provides three reasons for the advice to bear with those who think and act differently from oneself on matters of belief and practice. First, what people are doing, they are doing "in honor of the Lord" (14:6). Even though their practice may seem silly or just plain wrong to others of the same faith, when people eat or abstain, when they observe a day or ignore it, they are nonetheless seeking by their actions to honor the Lord Jesus Christ.
Paul's second reason is related to the first. Christians bear with one another not only because all are trying by their actions to honor Christ but also because Christ is, in fact, Lord of all, all the time. Even if Romans 14:1-6 seems to be discussing trivial things, Romans 14:7-9 cannot be. "If we live, we live to the Lord, and if we die, we die to the Lord; so then, whether we live or whether we die, we are the Lord's. For to this end Christ died and lived again, so that he might be Lord of both the dead and the living" (verses 8-9).
Christ died and rose in order to create community across the most fundamental of differences: Jew/Greek, slave/free, dead/living! The acknowledgement that Jesus is Lord implies a critique of all other powers, even the power of our most thoughtful, considered judgment on how to honor our Lord.
Paul's third reason for bearing with those whose practice differs from ours is that God is judge of all of us, and one judge is enough. We are not judges of each other. In contemporary American culture, this text, as well as Jesus' words in the Sermon on the Mount, "Do not judge, so that you may not be judged" (Matthew 7:1), are often taken to mean that all behavior is equally ethical, but neither text says such a thing.
In the film, Jesus of Montreal, when Daniel is explaining to his court-appointed psychiatrist why he made a whip of electrical cords and drove leering TV commercial producers from an audition they were shooting, he explains that he was reacting against the way the men disrespected the women they were auditioning. "I don't like contempt," he says.
The judgment forbidden in Romans 14 and Matthew 7 is the easy, contemptuous dismissal of those who do not believe like us, or vote like us, or live like us. They are fools, we think, and we see no contradiction between our being Christian and our despising of them (cf. Romans 10b).
Paul says no to such despising, as Jesus had. In Romans 14:17-19, Paul offers his alternative vision of Christian community. Given that these verses are nowhere in the Revised Common Lectionary, preachers of Romans 14:1-8 may want to work with later verses in the chapter as well. In verse 17, Paul observes, "For the Kingdom of God is not food and drink but righteousness and peace and joy in the Holy Spirit." With the gifts of righteousness, peace, and joy in the Spirit, the church can abide a lot of disagreement over many other things.