Very close friendship is spoken of as if it were binding together the souls of two people. This can be stated in active form. Alternate translation: "Jonathan felt a strong affection towards David" or "Jonathan committed himself to David" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-activepassive]])
Here "loved" refers to the love between friends, not romantic love. The word "soul" represents the person or the person's life. Alternate translation: "Jonathan loved David as much as he loved himself" or "Jonathan loved David as he loved his own life" (See: [[rc://en/ta/man/translate/figs-synecdoche]])