# day and night
This merism refers to "all the time" or "continually." (See: [[rc://en/ta/man/translate/figs-merism]])
# let your heart be true
"be wholly devoted"
# walk in his statutes
The way a person lives is spoken of as if that person were walking on a path. AT: "always obey his statutes" (See: [[rc://en/ta/man/translate/figs-metaphor]])