It is not clear exactly what Paul means with this phrase. He could be warning believers that they can fall into the same sins as the brother which they hope to help.1 Alternately, he could be warning believers not to become proud, thinking that they are better than those who have been caught up in sin.2
1 Brothers, if anyone is caught in any transgression, you who are spiritual should restore him in a spirit of gentleness. Keep watch on yourself, lest you too be tempted.