Romans 14:1 (KJV) Him that is weak in the faith receive ye, but not to doubtful disputations.
Here is the general principle Paul teaches. In vs 2-6 he gives two examples of matters which believers may disagree. His purpose is to show that Christians are to be helpers of each other, not judges. Each believer should accept all other believers who are trying to live for Christ.
Believers must judge evil behavior, but not condemn fellow believers who disagree with them about comparatively unimportant matters. Separation from other believers over such matters is utterly wrong. Of course there are fundamental truths of the faith which must be preached and defended even at the cost of separation from other Christians who reject them. But Paul is not speaking of these matters here in this chapter.
One who is “weak in the faith” is one who tends to have a sensitive conscience. They may not have as much knowledge of the freedom we have in Christ as you may. This is common among young believers – people who have just become saved. We are not to castigate them and make them feel ashamed, no. We welcome them and teach them, and encourage them as they grow.
Know Your Bible 