The Catechism of the Catholic Church (CCC):
Official Church Documents:
- Gaudium et Spes, Pastoral Constitution on the Church in the Modern World, Vatican Council II, Paragraph 27.
- Baltimore Catechism, Lesson 15, Paragraphs 189-193
- CatholicPhilly.com – Love of God and Love of Neighbor are the Heart of the Christian life
- Biography of Saint Teresa of Calcutta