In First Corinthians, chapter seven, Paul shifts from dealing with issues brought to his attention through various reports, and turns to answering questions contained in a letter written to him by believers in Corinth.  This is not a theological treatise on marriage and sexuality, but does address specific questions that dealt with those subjects.  Paul presents right up front the obligation of sexual relations between husbands and wives while, at the same time, encouraging those who are single to remain single and celibate if God has given them the gift of self-control.