John Calvin on Ephesians 5:19

19. To psalms, and hymns, and spiritual songs. These are truly pleasant and delightful fruits. The Spirit means “joy in the Holy Ghost,” (Romans 14:17;) and the exhortation, be ye filled, (ver. 18,) alludes to deep drinking, with which it is indirectly contrasted. Speaking to themselves, is speaking among themselves. Nor does he enjoin them to sing inwardly or alone; for he immediately adds, singing in your hearts; as if he had said, “Let your praises be not merely on the tongue, as hypocrites do, but from the heart.” What may be the exact difference between psalms and hymns, or between hymns and songs, it is not easy to determine, though a few remarks on this subject shall be offered on a future occasion. See Calvin Commentary on Philippians, Colossians, etc., page217. The appellation spiritual, given to these songs, is strikingly appropriate; for the songs most frequently used are almost always on trifling subjects, and very far from being chaste.