People consider the "heart" the center of emotions and the "tongue" voices those emotions. Alternate translation: "I was glad and rejoiced" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
Possible meanings of the words "my flesh" are 1) they indicate that the writer is a mortal who will die. Alternate translation: "even though I am only mortal, I will have confidence in God" or 2) they are a synecdoche for the writer's entire person. Alternate translation: "I will live with confidence in God" (See: [[rc://en/ta/man/translate/figs-synecdoche]])