Romans 12:9-13 deal with the importance of demonstrating love to fellow believers, and Romans 12:14-21 broaden this responsibility to include wider application to non-believers. Note the similarity with Jesus" instructions in the Sermon on the Mount ( Matthew 5-7). [source][source][source]
"From the thought of humility the idea of love naturally follows, for humility will necessarily express itself in affection for those around." [1][source]
Love for fellow believers12:9-13[source]
"Nowhere else in Paul"s writings do we find a more concise collection of ethical injunctions. In these five verses are thirteen exhortations ranging from love of Christians to hospitality for strangers. There are no finite verbs in the paragraph. There are, however, ten participles that serve as imperatives. In the three other clauses ( Romans 12:9-11) an imperative must be supplied. Each of the thirteen exhortations could serve as the text for a full-length sermon. What they deal with are basic to effective Christian living." [2][source]