The writer speaks of his words preserving a person's life as if they were that person's life. AT: "my words give life" or "the things I say give life" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The writer speaks of fully understanding his words as if the person searches for them and finds them. AT: "to those who understand and practice them" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The word "their" refers to "those who find them." The subject for this phrase can be supplied from the previous phrase. AT: "my words will give health to the whole body of those who find them" (See: [[rc://en/ta/man/translate/figs-ellipsis]])