Each realm grows out of the one before it. The first realm of heart is children's love. When we receive love and guidance from our parents, we can become good people. The second realm of heart is the love between brothers and sisters. Brothers and sisters who have the same parents have many things in common.
Parental love helps the children to get along with each other.
When we recognize that we all are children of the same heavenly Parent, we can live and work together in harmony. The third realm of heart is the love between husband and wife. A young man should grow up to be like our Heavenly Father, and a young woman should grow up to be like our Heavenly Mother. When they get married and learn to love each other, they become one, completing the circle of God's love. The fourth realm of heart is the love of parents.