Based on James 4:15, is it mandatory or optional to use the term “Lord willing” before stating future plans?
Regarding any future plans we may have as believers, it is not strictly necessary to say, “If the Lord wills” (Jas. 4:15). Even James says we “ought” to do it, not that we must. In addition, James is concerned here about our boasting (James 4:13-17), not requiring a formula we must scrupulously remember to say if God is to hear and answer our prayers.
James is warning about arrogance and presumption because we never know that we’ll have the rest of this day, let alone the next week, month or year(s). Saying “the Lord willing” is a good periodic reminder to ourselves and others to keep in mind the fleeting nature of our lives here on earth and that we must all—sooner or later—render an account to the Lord at our respective particular judgments (see CCC 1021-22).
However, if, for example, in a secular work environment, we always say “the Lord willing” whenever we receive a directive from our boss, we might quickly annoy our boss and coworkers and thereby undermine our witness, making ourselves and our misguided piety the focus instead of our accountability to the Lord. After all, our boss and coworkers realize that if you’re truly incapacitated or deceased, you won’t be able to carry out a directive.
So be at peace (see John 14:27) and remember that if you’re a faithful disciple, “the Lord willing” is always at least implicit regarding whatever you plan to do.