Here "heart" is a metonym for person's thoughts, feelings, or inner being. These three phrases are used together to mean "completely" or "earnestly." (See: [[rc://en/ta/man/jit/figs-metonymy]])
This simile compares how people are to love each other with the same love that they love themselves. Alternate translation: "to love your neighbor as much as you love yourself" (See: [[rc://en/ta/man/jit/figs-simile]])
This idiom means that something is more important than something else. In this case, these two commandments are more pleasing to God that burnt offering and sacrifices. This may be written clearly. Alternate translation: "is even more important than" or "is even more pleasing to God than" (See: [[rc://en/ta/man/jit/figs-idiom]])