Many people today believe that a week starts on Sunday and ends on Saturday, however, there are still other people believe that a week starts on Monday and ends on Sunday. ISO 8601 (http://en.wikipedia.org/wiki/ISO_8601#General_principles) defined Monday to be the first day of the week. What does the Bible say about which day is the first day of a week? Since the Bible have much much more authority than the so called ISO 8601, if the Biblical definition of the beginning of a week is different from the ISO 8601 definition, people should revise ISO 8601 according to the Bible, am I right?
People have numerous odd and useless ideas. This is one that I would categorize as useless as daylight savings time. For Christians, the day of worship is the first day of the week; just as Israel worshiped on the seventh-day of the week. What those days are named doesn't matter. Trying to deny reality and claim that the beginning of the work week is the beginning of the week will only produce confusion and for most Christian, a rejection of putting secular things higher than spiritual things.
Fortunately, ISO 8601 is only for communications purposes and can be ignored by the most of us.