In the administration of an oath, the word "swear" may be omitted, and the word "affirm" substituted, when the person to whom the obligation is administered is religiously scrupulous of swearing, or taking an oath in the prescribed form; and, in such case, the words "so help you God" may be omitted, and the words "under the pains and penalties of perjury" substituted; and a person so affirming shall be considered, for every legal purpose of privilege, qualification, or liability, as having been duly sworn.