You can make the full meaning explicit. You can also translate this in an active form. AT: "Let each person be sure what he is doing is to honor the Lord" (See: [[rc://en/ta/man/translate/figs-explicit]])
Here "observes" refers to worshiping. AT: "The person who worships on a certain day does it to honor the Lord" (See: [[rc://en/ta/man/translate/figs-explicit]])
This is an ellipsis. You can include the missing words. AT: "the person who eats every kind of food does it to honor the Lord" (See: [[rc://en/ta/man/translate/figs-ellipsis]])
This is an ellipsis. You can include the missing words. AT: "The person who does not eat certain kinds of food does it to honor the Lord" (See: [[rc://en/ta/man/translate/figs-ellipsis]])